fix(xtream): preserve pending backups and restore positions atomically (#1873)

* fix(xtream): preserve pending backups and restore positions atomically

* fix(xtream): retain sparse duplicate playback metadata on restore

* fix(xtream): require atomic restore in SQLite capability gate

* fix(xtream): preflight atomic restore without changing storage

libs/shared/interfaces/src/lib/electron-api.interface.ts

@@ -1246,6 +1246,10 @@ export interface ElectronBridgeApi {
     dbGetAllPlaybackPositions: (
         playlistId: string
     ) => Promise<PlaybackPositionData[]>;
+    dbReplaceAllPlaybackPositions: (
+        playlistId: string,
+        items: ElectronBridgePlaybackPositionInput[]
+    ) => Promise<ElectronBridgeResult>;
     dbClearAllPlaybackPositions: (
         playlistId: string
     ) => Promise<ElectronBridgeResult>;