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/components/BaseChip.vue

@@ -0,0 +1,48 @@
+<template>
+  <span :class="['chip', `chip--${variant}`]" v-bind="$attrs">
+    <slot />
+  </span>
+</template>
+
+<script setup lang="ts">
+withDefaults(defineProps<{
+  variant?: 'default' | 'primary' | 'success' | 'warning' | 'error'
+}>(), { variant: 'default' })
+</script>
+
+<style scoped lang="scss">
+.chip {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-1);
+  padding: var(--space-1) var(--space-3);
+  border-radius: var(--radius-full);
+  font-size: var(--text-sm);
+  font-weight: 600;
+
+  &--default {
+    background: var(--color-surface-2);
+    color: var(--color-text-muted);
+  }
+
+  &--primary {
+    background: var(--color-primary);
+    color: var(--color-primary-fg);
+  }
+
+  &--success {
+    background: #d4edda;
+    color: #155724;
+  }
+
+  &--warning {
+    background: #fff3cd;
+    color: #856404;
+  }
+
+  &--error {
+    background: #f8d7da;
+    color: #721c24;
+  }
+}
+</style>