fix(discord): add Apple Music cover opt-in, show Paused state

- iTunes Search API calls are now gated behind enableAppleMusicCoversDiscord
  (default: false). No external requests to Apple are made unless the user
  explicitly enables the new opt-in toggle in Settings.
- When the toggle is flipped, Discord presence is immediately re-sent for
  the current track (coversSettingChanged bypasses the early-return guard).
- When paused, activity type switches to Playing (no auto-timer) and state
  text shows "Paused" instead of the artist name.
- New authStore field + setter; new Settings toggle shown only when Discord
  RPC is enabled; i18n keys added to all 7 languages.

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

src/locales/en.ts

@@ -438,6 +438,8 @@ export const enTranslation = {
     minimizeToTrayDesc: 'When closing the window, keep Psysonic running in the system tray instead of quitting.',
     discordRichPresence: 'Discord Rich Presence',
     discordRichPresenceDesc: 'Show the currently playing track on your Discord profile. Requires Discord to be running.',
+    discordAppleCovers: 'Fetch covers from Apple Music for Discord',
+    discordAppleCoversDesc: 'Sends the artist and album name to Apple\'s search API to find cover art for your Discord profile. Disabled by default for privacy.',
     nowPlayingEnabled: 'Show in Now Playing',
     nowPlayingEnabledDesc: 'Broadcast your currently playing track to the server\'s live listener view. Disable to stop sending playback data.',
     lyricsServerFirst: 'Prefer server lyrics',