fix: switch frontend login to authentik auth-code flow

frontend/src/pages/AuthCallbackPage.vue

@@ -0,0 +1,54 @@
+<template>
+  <div class="flex items-center justify-center min-h-[70vh]">
+    <el-card class="w-full max-w-md shadow-md">
+      <div class="text-center space-y-3">
+        <h1 class="text-xl font-bold text-gray-800">member.ose.tw</h1>
+        <p class="text-sm text-gray-500">正在處理登入結果...</p>
+        <el-alert
+          v-if="error"
+          :title="error"
+          type="error"
+          show-icon
+          :closable="false"
+        />
+      </div>
+    </el-card>
+  </div>
+</template>
+
+<script setup>
+import { onMounted, ref } from 'vue'
+import { useRoute, useRouter } from 'vue-router'
+import { useAuthStore } from '@/stores/auth'
+import { exchangeOidcCode } from '@/api/auth'
+
+const route = useRoute()
+const router = useRouter()
+const authStore = useAuthStore()
+const error = ref('')
+
+onMounted(async () => {
+  const code = route.query.code
+  const redirect = route.query.redirect || '/me'
+  if (!code || typeof code !== 'string') {
+    error.value = '缺少授權碼，請重新登入'
+    return
+  }
+
+  try {
+    const callbackUrl = `${window.location.origin}/auth/callback?redirect=${encodeURIComponent(redirect)}`
+    const res = await exchangeOidcCode(code, callbackUrl)
+    authStore.setToken(res.data.access_token)
+    await authStore.fetchMe()
+    router.replace(typeof redirect === 'string' ? redirect : '/me')
+  } catch (err) {
+    authStore.logout()
+    const detail = err.response?.data?.detail
+    if (detail === 'authentik_code_exchange_failed') {
+      error.value = '授權碼交換失敗，請重新登入'
+    } else {
+      error.value = '登入失敗，請稍後再試'
+    }
+  }
+})
+</script>