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/main/store.ts

@@ -0,0 +1,18 @@
+import Store from 'electron-store';
+
+interface AppSettings {
+  sidebarCollapsed: boolean;
+}
+
+let _store: Store<AppSettings> | null = null;
+
+export function getStore(): Store<AppSettings> {
+  if (!_store) {
+    _store = new Store<AppSettings>({
+      defaults: {
+        sidebarCollapsed: false,
+      },
+    });
+  }
+  return _store;
+}