fix(docs): cache public videos

[zahlekhan]

Summary

• change the homepage videos from preload="metadata" to preload="none"
• cache every public .mp4 response in the browser for 24 hours
• preserve the original video assets, autoplay, looping, sources, and accordion auto-advance behavior

Root cause

The public MP4 assets were served with immediate revalidation, so repeat visits could transfer the same video data again. Metadata preloading could also initiate requests independently of playback.

Impact

Repeat visits within the cache window can reuse local video responses, and the preload hint no longer independently requests metadata. Existing playback and accordion behavior remains unchanged.

Validation

• git diff --check
• pnpm exec eslint --rule 'prettier/prettier: off' on the changed source/config files
• pnpm --filter @openuidev/docs types:check
• pnpm --filter @openuidev/docs build
• verified runtime response includes Cache-Control: public, max-age=86400, immutable