feat: add API client and auth store

frontend/src/store/auth.ts

@@ -0,0 +1,39 @@
+import { useState, useEffect } from 'react'
+import { authApi } from '../api'
+
+export interface User {
+  id: number
+  username: string
+  email: string
+  is_active: boolean
+}
+
+// Simple module-level state (no external lib needed)
+let currentUser: User | null = null
+const listeners = new Set<() => void>()
+
+export function useAuth() {
+  const [user, setUser] = useState<User | null>(currentUser)
+  const [loading, setLoading] = useState(currentUser === null)
+
+  useEffect(() => {
+    const update = () => setUser(currentUser)
+    listeners.add(update)
+    if (currentUser === null) {
+      authApi.me()
+        .then((res) => { currentUser = res.data; listeners.forEach((l) => l()) })
+        .catch(() => { currentUser = null; listeners.forEach((l) => l()) })
+        .finally(() => setLoading(false))
+    }
+    return () => { listeners.delete(update) }
+  }, [])
+
+  const logout = async () => {
+    await authApi.logout()
+    currentUser = null
+    listeners.forEach((l) => l())
+    window.location.href = '/login'
+  }
+
+  return { user, loading, logout }
+}