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>

frontend/src/stores/auth.ts

@@ -0,0 +1,18 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import type { User } from '@/types'
+
+export const useAuthStore = defineStore('auth', () => {
+  // Bootstrapped from the SPA shell injected by SpaController
+  const user = ref<User | null>(
+    (window as unknown as Record<string, unknown>).__PF_USER__ as User | null ?? null
+  )
+
+  const isAuthenticated = computed(() => user.value !== null)
+
+  function setUser(u: User | null) {
+    user.value = u
+  }
+
+  return { user, isAuthenticated, setUser }
+})