fix: resolve PWA static file serving and button visibility issues

[daniel-sullivan]

Frontend changes:

• Update PWA button to show on production HTTPS domains
• Add timeout fallback for production domains when beforeinstallprompt doesn't fire
• Add modern mobile-web-app-capable meta tag (fixes deprecation warning)
• Improve console logging for debugging PWA conditions Backend changes:
• Add proper static file serving for PWA files (favicon.svg, manifest.json, og-image.svg)
• Add NoRoute handler to serve static files from dist directory
• Ensure all PWA assets are accessible at production URLs This fixes the 404 errors for PWA files and makes the install button appear on production domains like babelbridge.world

[codecov]

Codecov Report

❌ Patch coverage is 21.42857% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.57%. Comparing base (c3ca3c4) to head (d368986).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
api/server.go	15.78%	15 Missing and 1 partial ⚠️
frontend/src/components/AddToAppButton.tsx	33.33%	5 Missing and 1 partial ⚠️

❌ Your patch status has failed because the patch coverage (21.42%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (56.57%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #7      +/-   ##
==========================================
- Coverage   57.08%   56.57%   -0.52%     
==========================================
  Files          24       24              
  Lines        1948     1971      +23     
  Branches      105      108       +3     
==========================================
+ Hits         1112     1115       +3     
- Misses        808      826      +18     
- Partials       28       30       +2     

Flag	Coverage Δ
backend	56.57% <21.42%> (-0.52%)	⬇️
frontend	55.87% <33.33%> (-0.15%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
frontend/src/components/AddToAppButton.tsx	84.25% <33.33%> (-2.74%)	⬇️
api/server.go	60.46% <15.78%> (-12.67%)	⬇️

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