Remove ADS Mode functionality permanently

[thostetler]

Problem

ADS Mode toggle is no longer needed and should be permanently removed from the application.

Changes

• Removed ADS Mode toggle from navbar and account menu
• Removed ADS Mode state slice, hooks, and utilities
• Removed adsMode state injection from SSR
• Updated tests to reflect removal
• Preserved legacy app detection (ui.adsabs.harvard.edu → ASTROPHYSICS mode)
• Preserved d URL parameter functionality

[codecov]

Codecov Report

❌ Patch coverage is 77.55102% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.9%. Comparing base (7671b3c) to head (3b94483).

Files with missing lines	Patch %	Lines
src/pages/paper-form.tsx	26.7%	11 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #746     +/-   ##
========================================
- Coverage    72.3%   71.9%   -0.4%     
========================================
  Files         221     217      -4     
  Lines       24801   24410    -391     
  Branches     1462    1405     -57     
========================================
- Hits        17927   17541    -386     
+ Misses       6833    6832      -1     
+ Partials       41      37      -4     

Files with missing lines	Coverage Δ
src/components/ClassicForm/helpers.ts	98.3% <100.0%> (-<0.1%)	⬇️
src/components/NavBar/NavBar.tsx	96.7% <ø> (-0.1%)	⬇️
src/middleware.ts	94.7% <100.0%> (-<0.1%)	⬇️
src/ssr-utils.ts	67.5% <100.0%> (-0.2%)	⬇️
src/store/slices/index.ts	100.0% <ø> (ø)
src/store/store.ts	60.6% <ø> (-0.1%)	⬇️
src/store/types.ts	100.0% <ø> (ø)
src/utils/legacyAppDetection.ts	100.0% <100.0%> (ø)
src/pages/paper-form.tsx	69.7% <26.7%> (-3.9%)	⬇️

... and 2 files with indirect coverage changes

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