feat: add Last.fm tag rule editing (full CRUD)

[fiddur]

Summary

• Adds update capability for Last.fm auto-tagging rules end-to-end — previously only create and delete existed
• Adds inline edit UI to the Last.fm tag rules component on the data sources page
• Includes 9 integration tests for the new updateLastFmTagRule DB function

Changes

api-spec

• updateLastFmTagRuleBodySchema and updateLastFmTagRuleResponseSchema with all fields optional for partial updates

Backend

• updateLastFmTagRule DB function with dynamic SQL SET clause (only updates provided fields)
• PUT /lastfm/tag-rules/:id REST route with tag cleanup + retroactive reapplication
• update_lastfm_tag_rule MCP tool
• 9 new integration tests covering: single field update, multi-field update, merge gap update/clear, artist_names update, non-existent rule, empty update, match type change, persistence verification

Frontend

• EditableRuleRow component with inline edit mode (same pattern as ScreentimeCategoriesSettings)
• Edit/Cancel/Save buttons with useMutation for optimistic flow
• Full form with all rule fields: name, tag, match type/mode, track, artists (with chip UI), merge gap
• Dark mode and mobile responsive CSS

[codecov]

Codecov Report

❌ Patch coverage is 41.02564% with 92 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.43%. Comparing base (8d40f29) to head (402025f).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
apps/backend/src/lastfm-router.ts	0.00%	50 Missing ⚠️
apps/backend/src/mcp/lastfm-tools.ts	19.23%	42 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #282      +/-   ##
===========================================
+ Coverage    31.33%   31.43%   +0.09%     
===========================================
  Files          181      181              
  Lines        22861    22986     +125     
  Branches      1842     1856      +14     
===========================================
+ Hits          7163     7225      +62     
- Misses       15663    15727      +64     
+ Partials        35       34       -1     

Flag	Coverage Δ
backend	58.08% <41.02%> (-0.25%)	⬇️

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