SCIX-813 feat(nav): add count badge to graphics menu item

[thostetler]

Summary

• Display figure count badge on the Graphics menu item in abstract side nav, matching the pattern used by Citations, References, Credits, and Mentions
• Add staleTime: 5min to useGetGraphicsCount to reduce redundant refetches when navigating between abstract subpages
• Fix latent MSW mock handler routing bug (':id' → '/:id')

Test plan

• Navigate to an abstract page with graphics — verify badge shows figure count
• Navigate to an abstract page without graphics — verify menu item is disabled, no badge
• Navigate between abstract subpages — verify graphics API is not re-called within 5 minutes
• pnpm test passes (890 tests, 0 failures)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.0%. Comparing base (a7a0d97) to head (7220a63).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #817     +/-   ##
========================================
+ Coverage    62.0%   62.0%   +0.1%     
========================================
  Files         317     317             
  Lines       36521   36522      +1     
  Branches     1642    1638      -4     
========================================
+ Hits        22608   22619     +11     
+ Misses      13876   13866     -10     
  Partials       37      37             

Files with missing lines	Coverage Δ
src/api/graphics/graphics.ts	76.7% <100.0%> (+8.3%)	⬆️
src/components/AbstractSideNav/AbstractSideNav.tsx	95.9% <100.0%> (ø)

... and 3 files with indirect coverage changes

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