[PB-6362] feature/Cloud sync

[CandelR]

Implements cloud photo metadata synchronization: now fetches the structure of the remote backup folder and stores file metadata locally in a new cloud_asset table. This enables the Photos timeline to show photos that exist in the cloud but have not yet been downloaded to the device ("cloud-only" items), with their thumbnails loaded on demand.

Summary

• PhotoCloudBrowser: new service that traverses the remote backup folder hierarchy and upserts file metadata into cloud_asset.
• cloud_asset: new table that stores remote file metadata (uuid, device id, creation date, filename, thumbnail bucket refs). Deduplicated against asset_sync at render time so already-backed-up photos don't appear twice.
• PhotoSyncStatus: extended with 'fetching-cloud'. The backup cycle now runs in order: cloud metadata fetch -> local discovery -> upload, so cloud-only items appear in the timeline before upload starts.
• Progressive timeline updates: cloudFetchRevision counter in Redux state increments after each month is fetched. usePhotosTimeline reacts to it so cloud-only items appear progressively month by month, without waiting for the upload phase to complete.
• Cloud thumbnails: useCloudThumbnail hook downloads and caches thumbnails for cloud-only items on demand.
• Sign out: signOutThunk clears both asset_sync and cloud_asset tables on logout.

[larryrider]

check sonarcloud issues

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.6% Duplication on New Code

See analysis details on SonarQube Cloud