feat: implement authors per result user preference

[thostetler]

Summary

• Add useAuthorsPerResult hook that reads the minAuthorsPerResult user preference
• Non-authenticated users see default of 4 authors
• Authenticated users see their configured preference (1-10)
• "all" preference (case-insensitive from vault) displays up to 50 authors (capped for UX)

Changes

• New: src/lib/useAuthorsPerResult.ts - Hook to get authors per result preference
• New: src/lib/__tests__/useAuthorsPerResult.test.tsx - 8 unit tests
• Modified: src/components/ResultList/Item/Item.tsx - Use hook in search results
• Modified: src/components/Libraries/DocumentList/DocumentItem.tsx - Use hook in library views

Test plan

• Manual test: non-authenticated user sees 4 authors
• Manual test: authenticated user with default sees 4 authors
• Manual test: change setting to 2, verify 2 authors shown
• Manual test: change setting to 10, verify 10 authors shown
• Manual test: verify in both search results and library views

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.9%. Comparing base (9678f94) to head (a407347).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #760     +/-   ##
========================================
+ Coverage    71.8%   71.9%   +0.1%     
========================================
  Files         217     218      +1     
  Lines       24485   24514     +29     
  Branches     1402    1406      +4     
========================================
+ Hits        17575   17603     +28     
- Misses       6878    6879      +1     
  Partials       32      32             

Files with missing lines	Coverage Δ
src/config.ts	100.0% <100.0%> (ø)
src/lib/useAuthorsPerResult.ts	100.0% <100.0%> (ø)

... and 1 file with indirect coverage changes

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