perf(audit): emojibase lazy-split, SW precache, Prism subset, lazy images

- emojibase (~965 KB) is now fully lazy: plugins/emoji.ts loads compact data +
  shortcode maps via a memoized dynamic import (rejections reset the memo so a
  mid-deploy chunk 404 can retry); reaction labels degrade to the raw glyph
  until loaded. Consumers get FRESH array references on load (the module arrays
  populate in place — same-ref state updates would skip re-render and leave
  emoji search empty; reviewer-caught). Verified out of the eager graph.
- Service worker precaches hashed assets (workbox precacheAndRoute, 82 entries
  ~10.8 MB incl. the crypto wasm): repeat visits stop re-downloading the app.
  index.html is NOT precached — navigations stay network-first so deploys are
  picked up immediately; the media-auth fetch handler is untouched.
- ReactPrism: curated 21-language set — chunk 574 KB → 71 KB.
- Timeline inline images get loading="lazy".
- Removed dead dompurify (+types); sanitize-html is the real sanitizer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/plugins/react-custom-html-parser.tsx

@@ -577,12 +577,12 @@ export const getReactCustomHtmlParser = (
             return (
               <span className={css.EmoticonBase}>
                 <span className={css.Emoticon()}>
-                  <img {...props} className={css.EmoticonImg} src={htmlSrc} />
+                  <img {...props} className={css.EmoticonImg} src={htmlSrc} loading="lazy" />
                 </span>
               </span>
             );
           }
-          if (htmlSrc) return <img {...props} className={css.Img} src={htmlSrc} />;
+          if (htmlSrc) return <img {...props} className={css.Img} src={htmlSrc} loading="lazy" />;
         }
       }