Add Last.fm auto-sync and fix auto-tagging

[fiddur]

Summary

• Auto-sync: Last.fm scrobbles are automatically synced before tag/daily-summary queries if the last sync is >30 minutes old (same pattern as Oura/RescueTime/Calendar)
• Retroactive tagging: New rules are applied to all existing scrobbles in raw_records
• Rule cleanup: Deleting a rule also removes its auto-generated tags
• Full re-tag: New POST /lastfm/retag endpoint and retag_lastfm_scrobbles MCP tool to delete all auto-tags and reapply all rules from scratch

Test plan

• Unit tests: 40 tests in lastfm-sync.test.ts (including new scrobbleRecordToScrobble, applyRuleRetroactively, cleanupRuleTags, retagAllScrobbles)
• Integration tests: 4 new tests in tags.integration.test.ts for hardDeleteTagsBySource and hardDeleteTagsByExternalIdPrefix
• All 854 tests pass across 50 test files
• Manual: Create a rule via MCP/REST and verify tags_applied > 0 for existing scrobbles
• Manual: Delete a rule and verify auto-tags are cleaned up
• Manual: Call retag_lastfm_scrobbles and verify full re-tag works
• Manual: Query tags and verify Last.fm auto-syncs when stale

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 37.09677% with 78 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.31%. Comparing base (01d66a5) to head (df20065).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
apps/backend/src/lastfm-router.ts	0.00%	29 Missing ⚠️
apps/backend/src/services/sync-provider.ts	0.00%	19 Missing ⚠️
apps/backend/src/db/raw-records.ts	7.69%	12 Missing ⚠️
apps/backend/src/mcp/lastfm-tools.ts	45.00%	11 Missing ⚠️
apps/backend/src/services/queries.ts	0.00%	6 Missing ⚠️
apps/backend/src/api.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #247      +/-   ##
===========================================
+ Coverage    27.26%   27.31%   +0.05%     
===========================================
  Files          176      176              
  Lines        23751    23863     +112     
  Branches      2122     2134      +12     
===========================================
+ Hits          6476     6519      +43     
- Misses       17236    17305      +69     
  Partials        39       39              

Flag	Coverage Δ
android	8.57% <ø> (ø)
backend	57.37% <37.09%> (-0.21%)	⬇️
web	3.02% <ø> (ø)

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