fix: weather icons in PWA + locale picker dropdown

- SW: skip cross-origin asset requests (opaque responses caused weather
  icons to break in PWA standalone mode on Android)
- Replace oikos-locale-picker radio buttons with <select> dropdown
- Add settings.localeLabel i18n key (de + en)
- Bump SW cache to v22

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

public/locales/en.json

@@ -510,6 +510,7 @@
     "googleDisconnectConfirm": "Disconnect Google Calendar?",
     "appleDisconnectConfirm": "Disconnect Apple Calendar?",
     "localeSystem": "System",
+    "localeLabel": "Language",
     "languageTitle": "Language"
   },