feat: add 6 new locales (ja, ko, fr, es, de, pt) and UI polish

- Add Japanese, Korean, French, Spanish, German, Portuguese translations
- Improve session active state visibility in both themes
- Static language labels in LanguageSwitch component
- Dark theme: lighten chat input background for better contrast
- Fix system theme listener not toggling back to light

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/client/src/i18n/index.ts

@@ -1,13 +1,32 @@
 import { createI18n } from 'vue-i18n'
 import en from './locales/en'
 import zh from './locales/zh'
+import ja from './locales/ja'
+import ko from './locales/ko'
+import fr from './locales/fr'
+import es from './locales/es'
+import de from './locales/de'
+import pt from './locales/pt'
 
 const saved = localStorage.getItem('hermes_locale')
 const detected = navigator.language.slice(0, 2)
 
+const supportedLocales = ['en', 'zh', 'ja', 'ko', 'fr', 'es', 'de', 'pt'] as const
+type SupportedLocale = (typeof supportedLocales)[number]
+
+function resolveLocale(saved: string | null, detected: string): SupportedLocale {
+  if (saved && (supportedLocales as readonly string[]).includes(saved)) {
+    return saved as SupportedLocale
+  }
+  if ((supportedLocales as readonly string[]).includes(detected)) {
+    return detected as SupportedLocale
+  }
+  return 'en'
+}
+
 export const i18n = createI18n({
   legacy: false,
-  locale: saved || (detected === 'zh' ? 'zh' : 'en'),
+  locale: resolveLocale(saved, detected),
   fallbackLocale: 'en',
-  messages: { en, zh },
+  messages: { en, zh, ja, ko, fr, es, de, pt },
 })