1.增加了重力感应，也就是横屏响应式布局。

2.修改了沉浸式布局。
3.修改了添加日程和编辑日程页面，增加了重复、提醒等功能。
4.修改了权限问题，如果日历本是只读，则有删除线做标识。同时，对于只读的日程，点击后将不再进入编辑页面，而是展示详情。
5.系统日历的处理。给用户两个选择，第一个选择就是只显示系统日历。第二种选择，用户可以选择一个caldav账户中的某一个日历本，把系统日历中的日程，包括日历日程和应用创建的日程，都读取出来，然后加入到这个日历本下，最后同步到caldav的服务器上，这样的好处是，手机丢失了，或者换了手机品牌型号，手机上的日程仍然在自己的caldav服务器上有一个备份。当然，系统日历中的caldav日历，就不会再读取了。

entry/src/main/ets/pages/SettingsPage.ets

@@ -1,19 +1,32 @@
 // entry/src/main/ets/pages/SettingsPage.ets
-// 设置页：系统日历混合显示开关 + 自动同步间隔
+// 设置页：系统日历模式（仅显示/备份到 CalDAV）+ 混合显示开关 + 自动同步间隔 + 后台同步
 import { router } from '@kit.ArkUI';
 import { common } from '@kit.AbilityKit';
 import { AppSettings } from '../common/AppSettings';
 import { BackgroundSyncService } from '../common/BackgroundSyncService';
+import { AccountStore, DavAccount } from '../common/AccountStore';
 import { LogUtil } from '../common/LogUtil';
 
 const INTERVAL_OPTIONS: number[] = [1, 5, 15, 30, 60];
 
+/** 日历本选项（备份目标 / 只读标记共用） */
+class BackupTarget {
+  calKey: string = '';
+  label: string = '';
+  serverWritable: boolean = true; // 服务器探测结果
+}
+
 @Entry
 @Component
 struct SettingsPage {
   @State showSystem: boolean = true;
   @State intervalMinutes: number = 1;
   @State backgroundSync: boolean = false;
+  @State sysMode: string = 'display'; // display | backup
+  @State backupKey: string = '';
+  @State backupTargets: BackupTarget[] = [];
+  @State allBooks: BackupTarget[] = []; // 全部 DAV 日历本（只读标记管理用）
+  @State manualKeys: string[] = [];     // 手动标记只读的 calKey
   private context?: common.Context;
 
   aboutToAppear(): void {
@@ -32,6 +45,128 @@ struct SettingsPage {
     AppSettings.getBackgroundSync(ctx).then((v: boolean): void => {
       this.backgroundSync = v;
     });
+    AppSettings.getSysCalMode(ctx).then((v: string): void => {
+      this.sysMode = v;
+    });
+    AppSettings.getManualReadonlyKeys(ctx).then((v: string[]): void => {
+      this.manualKeys = v;
+    });
+    this.loadBackupSettings();
+    this.loadAllBooks();
+  }
+
+  /** 加载全部 DAV 日历本（含探测到的写权限，只读标记管理用） */
+  private async loadAllBooks(): Promise<void> {
+    if (this.context === undefined) {
+      return;
+    }
+    const accounts: DavAccount[] = await AccountStore.loadAll(this.context);
+    const books: BackupTarget[] = [];
+    for (const acc of accounts) {
+      if (acc.type !== 'caldav') {
+        continue;
+      }
+      for (let i = 0; i < acc.calendarHrefs.length; i++) {
+        const b = new BackupTarget();
+        b.calKey = `${acc.id}_${i}`;
+        const bookName: string = i < acc.calendarNames.length ? acc.calendarNames[i] : `日历本 ${i + 1}`;
+        b.label = `${acc.name} · ${bookName}`;
+        b.serverWritable = acc.calendarWritable.length > i ? acc.calendarWritable[i] !== '0' : true;
+        books.push(b);
+      }
+    }
+    this.allBooks = books;
+  }
+
+  /** 手动标记/取消只读 */
+  private async toggleManualBook(b: BackupTarget): Promise<void> {
+    if (this.context === undefined) {
+      return;
+    }
+    const list: string[] = [...this.manualKeys];
+    const idx: number = list.indexOf(b.calKey);
+    if (idx >= 0) {
+      list.splice(idx, 1);
+    } else {
+      list.push(b.calKey);
+    }
+    this.manualKeys = list;
+    await AppSettings.setManualReadonlyKeys(this.context, list);
+    await this.loadBackupSettings(); // 备份目标候选同步排除
+    this.getUIContext().getPromptAction().showToast({
+      message: idx >= 0 ? '已恢复为可写，返回首页生效' : '已标记为只读，返回首页生效'
+    });
+  }
+
+  /** 日历本当前只读状态文案 */
+  private bookStateLabel(b: BackupTarget): string {
+    if (this.manualKeys.includes(b.calKey)) {
+      return '只读（手动）';
+    }
+    return b.serverWritable ? '可写' : '只读';
+  }
+
+  /** 加载备份目标候选（可写 DAV 日历本）+ 当前选择 */
+  private async loadBackupSettings(): Promise<void> {
+    if (this.context === undefined) {
+      return;
+    }
+    const accounts: DavAccount[] = await AccountStore.loadAll(this.context);
+    const targets: BackupTarget[] = [];
+    for (const acc of accounts) {
+      if (acc.type !== 'caldav') {
+        continue;
+      }
+      for (let i = 0; i < acc.calendarHrefs.length; i++) {
+        const writable: boolean = acc.calendarWritable.length > i
+          ? acc.calendarWritable[i] !== '0' : true;
+        if (!writable) {
+          continue;
+        }
+        const t = new BackupTarget();
+        t.calKey = `${acc.id}_${i}`;
+        const bookName: string = i < acc.calendarNames.length ? acc.calendarNames[i] : `日历本 ${i + 1}`;
+        t.label = `${acc.name} · ${bookName}`;
+        t.serverWritable = writable;
+        targets.push(t);
+      }
+    }
+    // 手动标记只读的本不可作为备份目标
+    const manual: string[] = await AppSettings.getManualReadonlyKeys(this.context);
+    this.backupTargets = targets.filter((t: BackupTarget): boolean => !manual.includes(t.calKey));
+    this.backupTargets = targets;
+    const saved: string = await AppSettings.getBackupCalKey(this.context);
+    this.backupKey = targets.some((t: BackupTarget): boolean => t.calKey === saved) ? saved : '';
+  }
+
+  private async saveSysMode(mode: string): Promise<void> {
+    if (this.context === undefined) {
+      return;
+    }
+    this.sysMode = mode;
+    await AppSettings.setSysCalMode(this.context, mode);
+    if (mode === 'backup' && this.backupKey === '') {
+      // 自动选中第一个可写日历本
+      if (this.backupTargets.length > 0) {
+        this.backupKey = this.backupTargets[0].calKey;
+        await AppSettings.setBackupCalKey(this.context, this.backupKey);
+      }
+    }
+    this.getUIContext().getPromptAction().showToast({
+      message: mode === 'backup'
+        ? '已开启备份：下次同步时把系统本地日程导入所选日历本'
+        : '已切换为仅显示：不再把系统日程备份到 CalDAV'
+    });
+  }
+
+  private async saveBackupTarget(calKey: string): Promise<void> {
+    if (this.context === undefined) {
+      return;
+    }
+    this.backupKey = calKey;
+    await AppSettings.setBackupCalKey(this.context, calKey);
+    this.getUIContext().getPromptAction()
+      .showToast({ message: '备份目标已更新，下次同步生效' });
   }
 
   private async saveShowSystem(value: boolean): Promise<void> {
@@ -96,7 +231,125 @@ struct SettingsPage {
 
       Scroll() {
         Column({ space: 12 }) {
-          // 系统日历混合显示
+          // 系统日历模式：仅显示 / 备份到 CalDAV
+          Column({ space: 8 }) {
+            Row({ space: 10 }) {
+              Column({ space: 2 }) {
+                Text('系统日历')
+                  .fontSize(15)
+                  .fontWeight(FontWeight.Medium)
+                  .fontColor($r('app.color.text_primary'))
+                Text('选择手机系统日历日程的处理方式')
+                  .fontSize(12)
+                  .fontColor($r('app.color.text_secondary'))
+              }
+              .alignItems(HorizontalAlign.Start)
+              .layoutWeight(1)
+            }
+            .width('100%')
+            Select([{ value: '仅显示（不做备份）' }, { value: '备份到 CalDAV 日历本' }] as SelectOption[])
+              .selected(this.sysMode === 'backup' ? 1 : 0)
+              .value(this.sysMode === 'backup' ? '备份到 CalDAV 日历本' : '仅显示（不做备份）')
+              .fontColor($r('app.color.text_primary'))
+              .font({ size: 14 })
+              .optionFont({ size: 14 })
+              .selectedOptionFont({ size: 14 })
+              .width('100%')
+              .onSelect((index: number) => {
+                const mode: string = index === 1 ? 'backup' : 'display';
+                if (mode !== this.sysMode) {
+                  this.saveSysMode(mode);
+                }
+              })
+            if (this.sysMode === 'backup') {
+              Text(this.backupTargets.length > 0
+                ? '备份目标（可写日历本）：导入后随同步上传服务器，换机/丢失也有备份'
+                : '没有可写的 CalDAV 日历本，请先添加账号或检查日历本权限')
+                .fontSize(12)
+                .fontColor(this.backupTargets.length > 0
+                  ? $r('app.color.text_secondary') : $r('app.color.error'))
+                .width('100%')
+              if (this.backupTargets.length > 0) {
+                Select(this.backupTargets.map((t: BackupTarget): SelectOption => {
+                  return { value: t.label } as SelectOption;
+                }) as SelectOption[])
+                  .selected(this.backupTargets.findIndex((t: BackupTarget): boolean => t.calKey === this.backupKey))
+                  .value(this.backupTargets.find((t: BackupTarget): boolean => t.calKey === this.backupKey)?.label
+                    ?? '请选择日历本')
+                  .fontColor($r('app.color.text_primary'))
+                  .font({ size: 14 })
+                  .optionFont({ size: 14 })
+                  .selectedOptionFont({ size: 14 })
+                  .width('100%')
+                  .onSelect((index: number) => {
+                    if (index >= 0 && index < this.backupTargets.length) {
+                      this.saveBackupTarget(this.backupTargets[index].calKey);
+                    }
+                  })
+              }
+            }
+          }
+          .alignItems(HorizontalAlign.Start)
+          .width('100%')
+          .padding(14)
+          .borderRadius(12)
+          .backgroundColor($r('app.color.card_bg'))
+          .border({ width: 1, color: $r('app.color.shadow_color') })
+
+          // 日历本只读标记（部分服务器不在 CalDAV 层拒绝写入，自动探测无法区分时手动标记）
+          Column({ space: 8 }) {
+            Row({ space: 10 }) {
+              Column({ space: 2 }) {
+                Text('日历本只读标记')
+                  .fontSize(15)
+                  .fontWeight(FontWeight.Medium)
+                  .fontColor($r('app.color.text_primary'))
+                Text('点击日历本切换只读标记：标记后其中日程仅可查看详情，新建日程时不再显示')
+                  .fontSize(12)
+                  .fontColor($r('app.color.text_secondary'))
+              }
+              .alignItems(HorizontalAlign.Start)
+              .layoutWeight(1)
+            }
+            .width('100%')
+            if (this.allBooks.length === 0) {
+              Text('暂无 CalDAV 日历本')
+                .fontSize(12)
+                .fontColor($r('app.color.text_hint'))
+                .width('100%')
+            }
+            ForEach(this.allBooks, (b: BackupTarget) => {
+              Row({ space: 8 }) {
+                Text(b.label)
+                  .fontSize(13)
+                  .fontColor($r('app.color.text_primary'))
+                  .maxLines(1)
+                  .textOverflow({ overflow: TextOverflow.Ellipsis })
+                  .layoutWeight(1)
+                Text(this.bookStateLabel(b))
+                  .fontSize(11)
+                  .fontColor(this.bookStateLabel(b) === '可写'
+                    ? $r('app.color.success') : $r('app.color.error'))
+                  .padding({ left: 8, right: 8, top: 3, bottom: 3 })
+                  .borderRadius(10)
+                  .backgroundColor(this.bookStateLabel(b) === '可写'
+                    ? $r('app.color.success_bg') : $r('app.color.error_bg'))
+              }
+              .width('100%')
+              .padding({ top: 6, bottom: 6 })
+              .onClick(() => {
+                this.toggleManualBook(b);
+              })
+            }, (b: BackupTarget) => `${b.calKey}_${this.manualKeys.includes(b.calKey) ? 1 : 0}`)
+          }
+          .alignItems(HorizontalAlign.Start)
+          .width('100%')
+          .padding(14)
+          .borderRadius(12)
+          .backgroundColor($r('app.color.card_bg'))
+          .border({ width: 1, color: $r('app.color.shadow_color') })
+
+          // 混合显示系统日历
           Row({ space: 10 }) {
             Column({ space: 2 }) {
               Text('混合显示系统日历')