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>

.eslintrc.json

@@ -12,5 +12,16 @@
     "plugin:import/electron",
     "plugin:import/typescript"
   ],
-  "parser": "@typescript-eslint/parser"
+  "parser": "@typescript-eslint/parser",
+  "settings": {
+    "import/resolver": {
+      "typescript": {
+        "alwaysTryTypes": true,
+        "project": "./tsconfig.json"
+      },
+      "node": {
+        "extensions": [".js", ".jsx", ".ts", ".tsx"]
+      }
+    }
+  }
 }