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/recent-emoji.test.ts

@@ -3,7 +3,7 @@ import assert from 'node:assert/strict';
 import { MatrixClient, MatrixEvent } from 'matrix-js-sdk';
 import { addRecentEmoji, getRecentEmojis, IRecentEmojiContent } from './recent-emoji';
 import { AccountDataEvent } from '../../types/matrix/accountData';
-import { emojis } from './emoji';
+import { emojis, loadEmojiData } from './emoji';
 
 // A Map-backed MatrixClient stub supporting get/setAccountData.
 const createMx = () => {
@@ -25,6 +25,9 @@ const createMx = () => {
 const getStored = (store: Map<string, unknown>): IRecentEmojiContent['recent_emoji'] =>
   (store.get(AccountDataEvent.ElementRecentEmoji) as IRecentEmojiContent | undefined)?.recent_emoji;
 
+// Emoji data is now loaded lazily; populate `emojis` before the round trips.
+await loadEmojiData();
+
 // Pick two real unicode emojis to drive add->get round trips.
 const u1 = emojis[0].unicode;
 const u2 = emojis[1].unicode;