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/Repository/UserRepository.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Repository;
+
+use App\Entity\User;
+use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
+use Doctrine\Persistence\ManagerRegistry;
+use Symfony\Component\Security\Core\Exception\UnsupportedUserException;
+use Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface;
+use Symfony\Component\Security\Core\User\PasswordUpgraderInterface;
+
+/**
+ * @extends ServiceEntityRepository<User>
+ */
+class UserRepository extends ServiceEntityRepository implements PasswordUpgraderInterface
+{
+    public function __construct(ManagerRegistry $registry)
+    {
+        parent::__construct($registry, User::class);
+    }
+
+    public function upgradePassword(PasswordAuthenticatedUserInterface $user, string $newHashedPassword): void
+    {
+        if (!$user instanceof User) {
+            throw new UnsupportedUserException(sprintf('Instances of "%s" are not supported.', $user::class));
+        }
+
+        $user->setPassword($newHashedPassword);
+        $this->getEntityManager()->persist($user);
+        $this->getEntityManager()->flush();
+    }
+}