feat: US-004 — App shell layout and sidebar navigation

- Add electron-store@8 for sidebar collapse state persistence via settings tRPC router
- Add @fontsource/geist for self-hosted Geist font (remove Google Fonts CDN)
- Add right-edge vertical 'keep scrolling for AI' label with chevron-down in all views
- Wire AppShell collapse toggle to settings.setSidebarCollapsed tRPC mutation
- Fix ESLint config with eslint-import-resolver-typescript to resolve @/* path aliases

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

src/renderer/globals.css

@@ -1,3 +1,7 @@
+@import '@fontsource/geist/400.css';
+@import '@fontsource/geist/500.css';
+@import '@fontsource/geist/600.css';
+
 @tailwind base;
 @tailwind components;
 @tailwind utilities;
@@ -44,5 +48,3 @@
     overflow: hidden;
   }
 }
-
-/* Geist font — loaded via CDN in index.html */