feat(story-1.2): Vue 3 SPA scaffold, base component library, User entity, SpaController

Frontend:
- Vue 3 + Vite + TypeScript strict in frontend/; builds to public/build/
- Vue Router (hash-history, requiresAuth guard → /login) and Pinia
- Global SCSS design tokens with 6 full themes (Warm Craft, Playful Pop, Sage & Cream, Dusty Mauve, Ocean Dusk, Honey & Slate)
- Base components: BaseButton (5 variants), BaseInput (floating label, error state),
  BaseBottomSheet (slide-up, focus trap, tap-outside dismiss), BaseCard, BaseChip,
  BaseToast (2.5s auto-dismiss, aria-live polite), BottomNav (4 tabs, hides at 960px)
- Type stubs for all API shapes: User, Device, Image, StickerLayer, RenderedAsset, Token

Backend:
- SpaController catch-all serves public/build/index.html; excludes api/setup/token/login/register
- User entity (email+password+roles+theme); UserRepository with PasswordUpgrader
- SecurityController with /login, /logout, /register stubs; Twig login form
- security.yaml: form_login firewall, remember_me, role_hierarchy, access_control
- Migration: create user table

Verified: npm run build succeeds, GET / → 302 /login (unauthenticated)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Controller/SecurityController.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Controller;
+
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Attribute\Route;
+use Symfony\Component\Security\Http\Authentication\AuthenticationUtils;
+
+class SecurityController extends AbstractController
+{
+    #[Route('/login', name: 'app_login', methods: ['GET', 'POST'])]
+    public function login(AuthenticationUtils $authenticationUtils): Response
+    {
+        if ($this->getUser()) {
+            return $this->redirectToRoute('spa');
+        }
+
+        return $this->render('security/login.html.twig', [
+            'last_username' => $authenticationUtils->getLastUsername(),
+            'error' => $authenticationUtils->getLastAuthenticationError(),
+        ]);
+    }
+
+    #[Route('/logout', name: 'app_logout')]
+    public function logout(): never
+    {
+        throw new \LogicException('Handled by Symfony Security firewall.');
+    }
+
+    #[Route('/register', name: 'app_register', methods: ['GET', 'POST'])]
+    public function register(): Response
+    {
+        // Implemented in Story 1.3
+        return $this->render('security/register.html.twig');
+    }
+}