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>

package.json

@@ -37,6 +37,7 @@
     "drizzle-kit": "^0.31.9",
     "electron": "40.6.0",
     "eslint": "^8.57.1",
+    "eslint-import-resolver-typescript": "^4.4.4",
     "eslint-plugin-import": "^2.32.0",
     "postcss": "^8.5.6",
     "tailwindcss": "^3.4.19",
@@ -44,6 +45,7 @@
     "vite": "^5.4.21"
   },
   "dependencies": {
+    "@fontsource/geist": "^5.2.8",
     "@tanstack/react-query": "^5.90.21",
     "@tanstack/react-router": "^1.161.1",
     "@trpc/client": "^11.10.0",
@@ -54,6 +56,7 @@
     "clsx": "^2.1.1",
     "drizzle-orm": "^0.45.1",
     "electron-squirrel-startup": "^1.0.1",
+    "electron-store": "^8.2.0",
     "electron-trpc": "^0.7.1",
     "framer-motion": "^12.34.2",
     "lucide-react": "^0.575.0",