fix(#51): firefox video loading reliability

[DSanich]

Summary

• Reduced unnecessary media auth preflight traffic by running checkMediaAuth only for protected, age-restricted media URLs.
• Added short-lived caching and in-flight request deduplication for media auth checks to avoid repeated HEAD calls for the same URL.
• Improved Firefox loading behavior by removing forced crossOrigin="anonymous" on media elements and limiting Firefox prefetch to image thumbnails (skipping video prefetch).

Avoid naming corporate partners, customers, or other sensitive external brands in this PR title or body. Use generic descriptors unless a maintainer explicitly approves the public reference.

Motivation

• Firefox users reported slower and less reliable video loading compared to Chromium-based browsers.
• The feed could trigger avoidable request overhead (auth preflight and video prefetch pressure), which increases startup latency and amplifies browser-specific networking differences.
• This change keeps protected-media behavior intact while reducing unnecessary network work for public media.

Related Issue

• Closes fix(firefox): improve video loading reliability #51

Testing

• npm run test
• Manual verification completed

Additional targeted checks run:

• npx vitest run src/components/VideoPlayer.test.tsx src/components/ThumbnailPlayer.test.tsx src/hooks/useAdultVerification.test.ts
• npx vitest run src/hooks/useVideoPrefetch.test.ts src/components/VideoPlayer.test.tsx src/components/VideoPlayer.authHeaders.test.tsx src/components/ThumbnailPlayer.test.tsx src/components/VideoGrid.test.tsx

Visuals

• UI change with screenshots/video attached
• No visual change
• Visuals and text avoid sensitive external brand or partner names unless explicitly approved

[github-actions]

🚀 Preview Deployment

Property	Value
Preview URL	https://59c1e639.divine-web-fm8.pages.dev
Commit	76bb478
Branch	fix/51-firefox-video-loading-reliability

[jalcine]

Closing per CONTRIBUTING.md - work on old issues needs re-alignment with current product direction before review. Please re-open with updated context if this is still relevant.