feat(chat): render native Twitch GIFs and optional GIF links - #3

Twitch's native GIF keyboard messages currently appear as text in the overlay. Render their GIFs inline using the documented IRC gifs ranges and preserve the complete media URL. Add two independent configurator/link options: native Twitch GIFs are on by default (gifs=0 disables them); direct GIPHY/Tenor image links are off by default (giflinks=1 enables them). Share-page URLs remain text.

Both paths use one visible-only loader, fit within 320 × 240 pixels and the overlay width, and fall back to the original text on failure. Allow only HTTPS GIF files on the specified provider image hosts, reject redirects, omit credentials/referrers, and use cache: no-store. Bound downloads to 5 MiB/10 seconds and validate GIF containers, dimensions and frame budgets before rendering. Leaving the viewport, fading, moderation and component disposal abort downloads and remove image elements/revoke blob URLs; final memory reclamation remains browser-managed. Update the option/host documentation and both privacy policies.

Validation:

• pnpm check and pnpm exec biome ci pass.
• pnpm build passes, including all five prerendered pages.
• Chromium 154 with controlled animated GIF responses: IRC-to-image flow with the supplied GIPHY URL unchanged, animation, narrow layouts, light/dark backgrounds, independent defaults, GIPHY/Tenor links, error fallback, lazy loading, moderation, fade cleanup, and cancellation before a response completes. No browser runtime errors.
• Live CDN responses could not be checked because this environment blocks GIPHY/Tenor hosts. Firefox/WebKit/OBS were not run locally.

Closes #2.