feat(landing): make landing page form selection sticky

[thostetler]

Summary

• Add user preference to remember the last-used search form (modern, classic, or paper) across sessions
• For authenticated users, preference is configurable in Settings
• For unauthenticated users, localStorage tracks the last-used form
• Only applies to Astrophysics discipline which has multiple form options

Changes

• Add LandingFormPreference enum with Auto/Modern/Classic/Paper options
• Create useLandingFormPreference hook to manage form preference
• Add Default Landing Page setting in application settings
• Track current form on each landing page mount
• Initialize localStorage synchronously to avoid double-render

Test plan

• Visit each landing page (modern, classic, paper) and verify form is tracked
• Check localStorage contains correct lastLandingForm value
• Log in and set preference in Settings > Search Settings
• Verify Start new search link respects the preference
• Verify non-Astrophysics modes always go to /

[codecov]

Codecov Report

❌ Patch coverage is 93.84615% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.8%. Comparing base (9678f94) to head (4d387cf).
⚠️ Report is 11 commits behind head on master.

Files with missing lines	Patch %	Lines
src/lib/useLandingFormPreference.ts	93.6%	7 Missing ⚠️
src/components/SearchBar/SearchBar.tsx	66.7%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #759     +/-   ##
========================================
+ Coverage    71.8%   71.8%   +0.1%     
========================================
  Files         217     221      +4     
  Lines       24485   24839    +354     
  Branches     1402    1421     +19     
========================================
+ Hits        17575   17830    +255     
- Misses       6878    6977     +99     
  Partials       32      32             

Files with missing lines	Coverage Δ
src/api/user/types.ts	100.0% <100.0%> (ø)
src/components/NavBar/NavBar.tsx	98.4% <100.0%> (+1.8%)	⬆️
src/pages/paper-form.tsx	70.1% <100.0%> (+0.5%)	⬆️
src/types.ts	100.0% <100.0%> (ø)
src/components/SearchBar/SearchBar.tsx	79.0% <66.7%> (+0.8%)	⬆️
src/lib/useLandingFormPreference.ts	93.6% <93.6%> (ø)

... and 10 files with indirect coverage changes

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[shinyichen]

A question about the code in the comment. Also, would it makes sense to update the upper left SicX link as well?

Otherwise looks good to me.

[thostetler]

would it makes sense to update the upper left SicX link as well?

yes, good idea -- I'll update and merge