feat: add React frontend - homepage, auth, products, craftsmen pages

- React 18 + Vite + TypeScript + TailwindCSS + shadcn/ui components
- Auth pages (login/register) with JWT token management via Zustand store
- Homepage with 9 craft category tiles (ceramics first, lacquerware second)
- METI 伝統的工芸品 badge and featured section on homepage
- Products page with category filters + METI認定 filter
- Craftsmen list page with METI badge display
- Navbar with auth-aware navigation
- Japanese warm color theme (amber/terracotta)
- API proxy config pointing to Express backend

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

client/src/store/auth.ts

@@ -0,0 +1,69 @@
+import { create } from 'zustand'
+import { api } from '@/lib/api'
+
+interface User {
+  id: string
+  email: string
+  role: string
+  first_name?: string
+  last_name?: string
+  display_name?: string
+  avatar_url?: string
+}
+
+interface AuthState {
+  user: User | null
+  token: string | null
+  isLoading: boolean
+  login: (email: string, password: string) => Promise<void>
+  register: (data: { email: string; password: string; role?: string; display_name?: string }) => Promise<void>
+  logout: () => void
+  checkAuth: () => Promise<void>
+}
+
+export const useAuthStore = create<AuthState>((set) => ({
+  user: null,
+  token: localStorage.getItem('token'),
+  isLoading: false,
+  
+  login: async (email, password) => {
+    set({ isLoading: true })
+    try {
+      const { user, token } = await api.post<{ user: User; token: string }>('/auth/login', { email, password })
+      localStorage.setItem('token', token)
+      set({ user, token, isLoading: false })
+    } catch (err) {
+      set({ isLoading: false })
+      throw err
+    }
+  },
+  
+  register: async (data) => {
+    set({ isLoading: true })
+    try {
+      const { user, token } = await api.post<{ user: User; token: string }>('/auth/register', data)
+      localStorage.setItem('token', token)
+      set({ user, token, isLoading: false })
+    } catch (err) {
+      set({ isLoading: false })
+      throw err
+    }
+  },
+  
+  logout: () => {
+    localStorage.removeItem('token')
+    set({ user: null, token: null })
+  },
+  
+  checkAuth: async () => {
+    const token = localStorage.getItem('token')
+    if (!token) return
+    try {
+      const user = await api.get<User>('/auth/me')
+      set({ user })
+    } catch {
+      localStorage.removeItem('token')
+      set({ user: null, token: null })
+    }
+  },
+}))