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/.gitignore

@@ -0,0 +1,24 @@
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+node_modules
+dist
+dist-ssr
+*.local
+
+# Editor directories and files
+.vscode/*
+!.vscode/extensions.json
+.idea
+.DS_Store
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?