i18n(settings): translate integrations section labels and placeholders

- Update Last.fm API key and shared secret labels
- Update Last.fm authorize button text
- Update ListenBrainz labels and token hint
- Add translations for connecting/opening states
- Add apiKey, sharedSecret, userToken translation keys

cc

src/lib/i18n/locales/en.json

@@ -577,6 +577,13 @@
       "disconnect": "Disconnect",
       "scrobbling": "Scrobbling",
       "configureApi": "Configure API",
+      "apiKey": "API Key",
+      "sharedSecret": "Shared Secret",
+      "userToken": "User Token",
+      "authorizeLastfm": "Authorize with Last.fm",
+      "opening": "Opening...",
+      "connecting": "Connecting...",
+      "listenbrainzTokenHint": "Get your personal token from",
       "musicbrainz": "MusicBrainz",
       "musicbrainzDesc": "Enable artist relationships and enhanced metadata from MusicBrainz.",
       "musicbrainzCache": "MusicBrainz Cache",