feat: demo 同步 is_first_install 维度并修复 preferences 落盘

- StartupDiagnostics 新增 is_first_install 维度展示：preferences 无启动记录视为安装后首启，随后写入标记并 flushSync 同步落盘（与生产 StartManager.getAppInstallStatus 语义等价，演示工程无 biz_common 依赖故自实现）
- 修复 putSync 仅写内存缓存不落盘的问题：force-stop 后数据丢失，二次启动误判为首启；对比 AuthSession.flushSync 用法定位根因
- EntryAbility 调用 initialize 时传入 UIAbilityContext
- 真机验证：安装/清数据后首启 is_first_install=true，二次启动=false；全场景 3 组（拦截/登录/冷启动/热启动/强杀/补报）24 断言全部通过，耗时 127~165ms

Co-Authored-By: Claude <noreply@anthropic.com>

CrashDiagnosticsDemo/entry/src/main/ets/diagnostics/StartupDiagnostics.ets

@@ -7,6 +7,7 @@ import { common } from '@kit.AbilityKit';
 import { inspector } from '@kit.ArkUI';
 import { hiAppEvent, hilog } from '@kit.PerformanceAnalysisKit';
 import { deviceInfo } from '@kit.BasicServicesKit';
+import { preferences } from '@kit.ArkData';
 
 enum DrawReportState {
   IDLE,
@@ -41,6 +42,11 @@ export class StartupDiagnostics {
    * watcher 注册时间戳（epoch ms），用于识别系统补投递的上次启动遗留事件。
    */
   private static watcherRegisterTime: number = 0;
+  /**
+   * 是否安装后首次启动（维度）：preferences 无启动记录即为首次，随后写入标记。
+   * 与生产实现（StartManager.getAppInstallStatus）语义等价，演示工程无 biz_common 依赖故自实现。
+   */
+  private static isFirstInstall: boolean = false;
   private static watcherInitialized: boolean = false;
   private static drawReportState: DrawReportState = DrawReportState.IDLE;
   private static capturedEntryPage: string = '未捕获';
@@ -57,10 +63,19 @@ export class StartupDiagnostics {
   private static lastAction: string = '等待登录页首次绘制';
   private static lastLaunchDetail: string = '尚未收到 APP_LAUNCH';
 
-  static initialize(): void {
+  static initialize(context: common.UIAbilityContext): void {
     if (StartupDiagnostics.watcherInitialized) {
       return;
     }
+    // 首次安装标志：preferences 无启动记录视为首次，随后写入并同步落盘；异常时按非首次处理
+    try {
+      const pref: preferences.Preferences = preferences.getPreferencesSync(context, { name: 'startup_demo' });
+      StartupDiagnostics.isFirstInstall = !pref.getSync('has_launched', false);
+      pref.putSync('has_launched', true);
+      pref.flushSync();
+    } catch (e) {
+      StartupDiagnostics.isFirstInstall = false;
+    }
 
     const filter: hiAppEvent.AppEventFilter = {
       domain: hiAppEvent.domain.OS,
@@ -273,6 +288,7 @@ export class StartupDiagnostics {
       `appattach_to_appforeground_dur=${appattachToAppForegroundDur}ms\n` +
       `device_type=${StartupDiagnostics.getDeviceType()}, ` +
       `system_version=${StartupDiagnostics.getSystemVersion()}\n` +
+      `is_first_install=${StartupDiagnostics.isFirstInstall}\n` +
       `补报事件=${isBackfill ? '是（entry_page 不归因，按 unknown 处理）' : '否'}`;
     StartupDiagnostics.lastAction = '已捕获有效冷启动 APP_LAUNCH';
     StartupDiagnostics.logInfo(StartupDiagnostics.lastLaunchDetail);

CrashDiagnosticsDemo/entry/src/main/ets/entryability/EntryAbility.ets

@@ -26,7 +26,7 @@ export default class EntryAbility extends UIAbility {
   onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
     try {
       CrashDiagnostics.initialize(this.context as common.UIAbilityContext);
-      StartupDiagnostics.initialize();
+      StartupDiagnostics.initialize(this.context as common.UIAbilityContext);
       AuthSession.initialize(this.context as common.UIAbilityContext);
       this.context.getApplicationContext().setColorMode(ConfigurationConstant.ColorMode.COLOR_MODE_NOT_SET);
     } catch (err) {