[FEATURE] Export/Backup & Restore of Metadata (Tags, Albums, Face Clusters)

[IshitaSingh0822]

Describe the feature

Problem

All smart-tagging, album, and face-cluster data lives only in the local SQLite
DB. If a user reinstalls, moves machines, or the DB gets corrupted, all
organization work (clusters, tags, albums) is lost — a major risk for a
"privacy-first" tool where data never leaves the device.

Proposed Solution

• Add GET /backup/export returning a portable JSON/SQLite dump of albums,
  tags, face cluster labels (not raw images).
• Add POST /backup/import to restore from such a file, with conflict handling
  (merge vs overwrite).
• Frontend: Settings page section "Backup & Restore" with export/import buttons.

Why this matters

• Data-loss protection is critical for local-only apps.
• Self-contained, well-scoped, touches DB layer + settings UI — good for a
  medium-difficulty contribution.

Acceptance Criteria

• Export produces versioned JSON schema
• Import validates schema version and merges safely
• Settings UI for export/import with success/error toasts
• Tests for round-trip export → import

Add ScreenShots

Happy to work on this if it aligns with the project's roadmap - would appreciate any guidance on schema versioning conventions before I start.
Thanks!

Record

• I agree to follow this project's Code of Conduct
• I want to work on this issue

[github-actions]

👋 Thanks for opening this issue! The maintainers will review it shortly. Till then, do not open any PR. This is a strict rule we like to follow around here :)