feat(i18n): add Ukrainian & Chinese, fix zh/uk translation quality

Add two new languages (uk, zh / zh_CN) across the extension and website:
register them in SUPPORTED_LANGUAGES, the Chrome _locales map, the website
build/lang-init/app routing, hreflang/og/schema tags and language selectors.

Fix systematic machine-translation word-sense errors in the new zh/uk
locales (e.g. zh "Status"=地位→状态, "Leave Room"=留出空间→离开房间,
"Play"=玩→播放, "Seek"=寻找→跳转, audio Attack/Release/Knee; uk "Play"=Грати
→Відтворити, "Clear"=ЯСНО→Очистити, "Open"=ВІДЧИНЕНО→Відкрити, peers
"Однолітки"→"Учасники"), translate remaining English leftovers (Room ID,
Custom) and normalise terminology. All 15 locales pass test-locales.cjs.

Note: popup.html and website/template.html also carry the language-selector
additions here; their Ko-Fi→Support label text is part of the branding change.

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

extension/locales/fr.json

@@ -181,7 +181,7 @@
   "LOBBY_CANCEL_TIMEOUT_PEERS_LOAD": "Délai dépassé — tous les membres n'ont pas chargé l'épisode",
   "LOBBY_CANCEL_USER": "Annulé par l'utilisateur",
   "NOTIF_ERROR_TITLE": "Erreur KoalaSync",
-  "FOOTER_SUPPORT": "☕ Offre-moi un café",
+  "FOOTER_SUPPORT": "Support KoalaSync",
   "FOOTER_REVIEW": "★ Évaluer",
   "FOOTER_SUPPORT_PROMPT": "Tu aimes KoalaSync? Laisse un avis!",
   "LABEL_AUDIO_PROCESSING": "Traitement audio",