Replace per-schedule count-based retention with unified tiered classification.
Backups are now classified by timestamp into categories (hourly/daily/weekly/monthly)
and are only deleted when they exceed ALL applicable category quotas.
Changes:
- Add backup-classification.service.ts for timestamp-based classification
- Rewrite backup-retention.service.ts with tiered logic
- Add categories and expires_at columns to backup_history
- Add Expires column to desktop and mobile backup UI
- Add unit tests for classification logic (22 tests)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
