- Add detection of server full resync indication (needs_full_resync flag or null last_sync_id)
- Add _clear_local_tracking() method to force full sync
- Modify needs_recovery() to check for full resync conditions
- Modify collect_report_data() to force full sync when needed
- Add comprehensive test suite for full resync scenarios
- Add implementation documentation

Handles cases where server indicates full resync is needed:
- Server responds with needs_full_resync=true
- Server responds with null last_sync_id
- Server returns 404 (no record for client)