feat: task 1.6 login page

src/ui/pages/login.tsx — LoginPage component:
- Centred card on muted background.
- shadcn Form + FormField with react-hook-form + zodResolver.
  FormMessage renders field-level zod errors automatically.
- Email + password with proper autocomplete attrs for password managers.
  autoFocus on email.
- Submit calls useAuthStore.getState().login(); errors render in a
  destructive Alert above the form.
- In-flight via the auth store's 'authenticating' status (cross-tab safe).
- onAuthenticated callback fires on store transition to authenticated;
  1.7 wires this to a router redirect.

src/App.tsx branches on auth status:
- unknown / authenticating -> "Signing you in..." placeholder
  (avoids flashing the login page on hard refresh while the boot probe
  runs)
- anonymous -> <LoginPage />
- authenticated -> home placeholder (1.7 replaces with router shell)

Deviation: skipped src/routes/login.tsx — requires the router plugin
to have generated routeTree.gen.ts, which is 1.7's territory. The page
works standalone via App.tsx's status branch.

Search-param redirect (?redirect=...) also deferred to 1.7 — no router
yet to expose useSearch. onAuthenticated callback is the seam.

.planning/ROADMAP.md

@@ -54,7 +54,7 @@ These rules govern every task. Any deviation must be discussed and documented as
 | 1.3  | [Vite dev proxy + path aliases + tsconfig hardening](./phase-1-foundation/03-vite-dev-proxy.md)              | 🟩     | `39b60c9` |
 | 1.4  | [Runtime config endpoint](./phase-1-foundation/04-runtime-config.md)                                         | 🟩     | `8e2151a` |
 | 1.5  | [Directus auth client (cookie mode + refresh)](./phase-1-foundation/05-directus-auth-client.md)              | 🟩     | `38fe2e3` |
-| 1.6  | [Login page](./phase-1-foundation/06-login-page.md)                                                          | ⬜     | —         |
+| 1.6  | [Login page](./phase-1-foundation/06-login-page.md)                                                          | 🟩     | `PENDING_SHA` |
 | 1.7  | [Routing skeleton (TanStack Router + role-aware guards)](./phase-1-foundation/07-routing-skeleton.md)        | ⬜     | —         |
 | 1.8  | [Logout flow](./phase-1-foundation/08-logout-flow.md)                                                        | ⬜     | —         |
 | 1.9  | [Gitea CI + Dockerfile + nginx static serve](./phase-1-foundation/09-gitea-ci-and-dockerfile.md)             | ⬜     | —         |