T5/Phase 3: SPA shell + navigation

- TanStack Router with type-safe file-based routes
- Sidebar: collapsible, workspace switcher, 12 nav links, user menu
- Topbar: search, quick-add, notifications, user avatar
- cmdk command palette: nav + create + search + @mentions
- Keyboard shortcuts: Cmd+K palette, g+t/h/p/n/c/g/s navigation, ? help
- Theme: dark default, accent picker (slate/blue/green/purple/orange), persisted to localStorage
- Auth: login -> /, logout -> /login, 401 redirect
- Placeholder pages for all 13 nav routes (real in T6/T7)
- Typed API client with useApiQuery/useApiMutation hooks

apps/web/src/routes/_app/notes.tsx

@@ -0,0 +1,17 @@
+import { createRoute } from "@tanstack/react-router";
+import { Route as appRoute } from "../_app";
+
+function NotesPage() {
+  return (
+    <div className="flex flex-col items-center justify-center min-h-[60vh]">
+      <h1 className="text-3xl font-bold mb-2">Notes</h1>
+      <p className="text-muted-foreground">Coming in T6 — notes and documents.</p>
+    </div>
+  );
+}
+
+export const Route = createRoute({
+  getParentRoute: () => appRoute,
+  path: "/notes",
+  component: NotesPage,
+});