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/index.css

@@ -24,6 +24,7 @@
     --input: 214.3 31.8% 91.4%;
     --ring: 222.2 84% 4.9%;
     --radius: 0.5rem;
+    --accent-hsl: 217 91% 60%;
   }
 
   .dark {
@@ -46,6 +47,7 @@
     --border: 217.2 32.6% 17.5%;
     --input: 217.2 32.6% 17.5%;
     --ring: 212.7 26.8% 83.9%;
+    --accent-hsl: 217 91% 60%;
   }
 }