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>

scripts/test-locales.cjs

@@ -128,7 +128,8 @@ const chromeLocalesDir = path.join(__dirname, '..', 'extension', '_locales');
 const chromeLocaleMap = {
   'en': 'en', 'de': 'de', 'fr': 'fr', 'es': 'es', 'it': 'it',
   'ja': 'ja', 'ko': 'ko', 'nl': 'nl', 'pl': 'pl',
-  'pt-BR': 'pt_BR', 'pt': 'pt_PT', 'ru': 'ru', 'tr': 'tr'
+  'pt-BR': 'pt_BR', 'pt': 'pt_PT', 'ru': 'ru', 'tr': 'tr',
+  'zh': 'zh_CN', 'uk': 'uk'
 };
 
 // Read SUPPORTED_LANGUAGES from i18n.js