feat(settings): collapse Discord sub-options under one header

"Fetch covers from Apple Music" and "Custom text templates" are now both
tucked into a single collapsible "Advanced Discord options" block (default
collapsed) that only appears when Discord Rich Presence is enabled.
Reduces vertical noise in Settings → General for the common case where
users just flip Rich Presence on and leave the defaults.

Uses the same chevron-rotate pattern as the font picker and contributors
list. Adds `settings.discordOptions` key in all 8 locales.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/en.ts

@@ -542,6 +542,7 @@ export const enTranslation = {
     useCustomTitlebarDesc: 'Replace the system title bar with a built-in one that matches the app theme. Disable to use the native GNOME/GTK title bar.',
     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.',
+    discordOptions: 'Advanced Discord options',
     discordTemplates: 'Custom text templates',
     discordTemplatesDesc: 'Customize what information is shown on your Discord profile. Variables: {title}, {artist}, {album}',
     discordTemplateDetails: 'Primary line (details)',