fix: clean up VSCode settings duplication and hide irrelevant sections

Remove mermaidRendering, userMessageRendering, stickyUserHeader from Appearance in VSCode (already in Chat)
Hide Navigation settings (navRail, terminalQuickKeys) in VSCode Appearance
Hide Shortcuts section entirely in VSCode

packages/ui/src/lib/settings/metadata.ts

@@ -158,6 +158,7 @@ export const SETTINGS_PAGE_METADATA: readonly SettingsPageMeta[] = [
     group: 'general',
     kind: 'single',
     keywords: ['keyboard', 'hotkeys', 'shortcuts', 'bindings'],
+    isAvailable: (ctx) => !ctx.isVSCode,
   },
   {
     slug: 'sessions',