feat: implement apiFetch wrapper and auth API calls

frontend/src/api/auth.ts

@@ -1 +1,45 @@
-// Auth API calls — implemented in Phase 2
+import { apiFetch } from './client'
+import type { AuthResponse } from '../types'
+
+export async function login(email: string, password: string): Promise<AuthResponse> {
+  const res = await apiFetch('/api/auth/login', {
+    method: 'POST',
+    body: JSON.stringify({ email, password }),
+  })
+  if (!res.ok) {
+    const err = await res.json()
+    throw new Error(err.detail ?? 'Login failed')
+  }
+  return res.json()
+}
+
+export async function signup(
+  full_name: string,
+  email: string,
+  password: string,
+  role: string,
+  class_code?: string
+): Promise<AuthResponse> {
+  const res = await apiFetch('/api/auth/signup', {
+    method: 'POST',
+    body: JSON.stringify({ full_name, email, password, role, class_code }),
+  })
+  if (!res.ok) {
+    const err = await res.json()
+    throw new Error(err.detail ?? 'Signup failed')
+  }
+  return res.json()
+}
+
+export async function logout(): Promise<void> {
+  await apiFetch('/api/auth/logout', { method: 'POST' })
+}
+
+export async function refreshToken(): Promise<{ access_token: string }> {
+  const res = await fetch('/api/auth/refresh', {
+    method: 'POST',
+    credentials: 'include',
+  })
+  if (!res.ok) throw new Error('Refresh failed')
+  return res.json()
+}

frontend/src/api/client.ts

@@ -0,0 +1,50 @@
+import { useAuthStore } from '../store/authStore'
+
+const API_BASE = ''
+
+async function refreshToken(): Promise<boolean> {
+  const res = await fetch(`${API_BASE}/api/auth/refresh`, {
+    method: 'POST',
+    credentials: 'include',
+  })
+  if (!res.ok) return false
+  const data = await res.json()
+  const { user } = useAuthStore.getState()
+  if (user) useAuthStore.getState().setAuth(data.access_token, user)
+  return true
+}
+
+export async function apiFetch(path: string, options: RequestInit = {}): Promise<Response> {
+  const token = useAuthStore.getState().accessToken
+
+  const res = await fetch(`${API_BASE}${path}`, {
+    ...options,
+    headers: {
+      'Content-Type': 'application/json',
+      ...(token ? { Authorization: `Bearer ${token}` } : {}),
+      ...options.headers,
+    },
+    credentials: 'include',
+  })
+
+  if (res.status === 401) {
+    const refreshed = await refreshToken()
+    if (!refreshed) {
+      useAuthStore.getState().clearAuth()
+      window.location.href = '/login'
+      return res
+    }
+    const newToken = useAuthStore.getState().accessToken
+    return fetch(`${API_BASE}${path}`, {
+      ...options,
+      headers: {
+        'Content-Type': 'application/json',
+        ...(newToken ? { Authorization: `Bearer ${newToken}` } : {}),
+        ...options.headers,
+      },
+      credentials: 'include',
+    })
+  }
+
+  return res
+}