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/__root.tsx

@@ -1,9 +1,11 @@
 import { createRootRoute, Outlet } from "@tanstack/react-router";
+import { TanStackRouterDevtools } from "@tanstack/react-router-devtools";
 
 export const Route = createRootRoute({
   component: () => (
     <div className="min-h-screen bg-background text-foreground">
       <Outlet />
+      {import.meta.env.DEV && <TanStackRouterDevtools />}
     </div>
   ),
 });