fix(core): 完善备份功能 - 增量跳过/外部数据/force-stop/取消修复

Phase 1: 基础架构
- app_details.json 元数据增强 (apk_version/Ssaid/permissions/Size/keystore/time)
- 备份前 force-stop 进程，确保数据库一致性
- 新增 Android/data 外部数据备份+恢复 (backupExternalData/restoreExternalData)

Phase 2: 增量优化
- APK 版本增量跳过 (对比 versionCode)
- 数据大小增量跳过 (对比旧 Size)

Phase 3: 完整度
- 路径防呆检查 (拒绝 Android/ 目录内备份)
- ! 前缀解析打通 (appList.txt 过滤)

修复:
- ResticStreamBackup: CancellationException 重新抛出
- ResticStreamBackup: Producer 添加 force-stop
- RestoreOperation: OBB/外部数据 SELinux context 修复
- ResticStreamBackup: 修复预存编译错误 (AppError.Config/AppError.Cancelled)

CLAUDE.md

@@ -1,7 +1,7 @@
 <!-- gitnexus:start -->
 # GitNexus — Code Intelligence
 
-This project is indexed by GitNexus as **android-backup-gui** (1736 symbols, 4185 relationships, 151 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
+This project is indexed by GitNexus as **android-backup-gui** (1734 symbols, 4049 relationships, 110 execution flows). Use the GitNexus MCP tools to understand code, assess impact, and navigate safely.
 
 > If any GitNexus tool warns the index is stale, run `npx gitnexus analyze` in terminal first.