feat:實作 Admin Panel — 平台管理後台

後端：
- AdminStatsController：總會員/教練/課程數統計 API
- AdminUserController：會員與教練列表、詳情、啟用/停用、教練驗證（toggle 反轉語意）
- AdminOfferController：全平台課程列表與刪除
- routes/api.php：新增 /api/admin/stats、members、providers、offers 等路由

前端（frontend/）：
- adminAuth store、adminAxios（第三套獨立認證）
- /admin/* 路由群組 + requiresAdmin guard
- AdminNavBar、AdminLayout
- App.vue：isCoachPage → isBackofficePage（/coach/* 和 /admin/* 皆隱藏會員 NavBar）
- LoginView、DashboardView（統計卡片）
- MembersView、ProvidersView（含驗證操作）、OffersView（含刪除確認）

OpenSpec：
- 新增 specs：admin-auth / admin-user-management / admin-offer-management / admin-stats / admin-panel-ui
- 歸檔：openspec/changes/archive/2026-05-10-admin-panel

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/admin/MembersView.vue

@@ -0,0 +1,87 @@
+<script setup>
+import { ref, onMounted } from 'vue'
+import adminApi from '../../api/adminAxios'
+
+const members = ref([])
+const loading = ref(true)
+const search  = ref('')
+
+async function fetchMembers() {
+  loading.value = true
+  try {
+    const params = {}
+    if (search.value) params.q = search.value
+    const res = await adminApi.get('/admin/members', { params })
+    members.value = res.data.data
+  } finally {
+    loading.value = false
+  }
+}
+
+async function toggleActive(member) {
+  try {
+    const res = await adminApi.put(`/admin/members/${member.id}/toggle-active`)
+    member.is_active = res.data.data.is_active
+  } catch (e) {
+    alert(e.response?.data?.message || '操作失敗')
+  }
+}
+
+onMounted(fetchMembers)
+</script>
+
+<template>
+  <main class="max-w-6xl mx-auto px-4 py-10">
+    <h1 class="text-2xl font-bold text-slate-800 mb-6">會員管理</h1>
+
+    <div class="flex gap-3 mb-6">
+      <input v-model="search" @keyup.enter="fetchMembers" type="text" placeholder="搜尋姓名或 Email..."
+        class="flex-1 border border-slate-300 rounded-lg px-4 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-slate-400" />
+      <button @click="fetchMembers"
+        class="bg-slate-800 text-white px-5 py-2 rounded-lg text-sm hover:bg-slate-700 transition">搜尋</button>
+    </div>
+
+    <div v-if="loading" class="text-center text-slate-400 py-20">載入中...</div>
+
+    <div v-else class="bg-white rounded-2xl shadow overflow-hidden">
+      <table class="w-full text-sm">
+        <thead class="bg-slate-50 text-slate-500 text-xs uppercase tracking-wide">
+          <tr>
+            <th class="px-6 py-3 text-left">姓名</th>
+            <th class="px-6 py-3 text-left">Email</th>
+            <th class="px-6 py-3 text-left">註冊時間</th>
+            <th class="px-6 py-3 text-center">狀態</th>
+            <th class="px-6 py-3 text-center">操作</th>
+          </tr>
+        </thead>
+        <tbody class="divide-y divide-slate-100">
+          <tr v-for="m in members" :key="m.id" class="hover:bg-slate-50">
+            <td class="px-6 py-4 font-medium text-slate-800">{{ m.name }}</td>
+            <td class="px-6 py-4 text-slate-500">{{ m.email }}</td>
+            <td class="px-6 py-4 text-slate-400 text-xs">{{ m.created_at?.slice(0,10) }}</td>
+            <td class="px-6 py-4 text-center">
+              <span :class="m.is_active
+                ? 'bg-green-100 text-green-700'
+                : 'bg-red-100 text-red-600'"
+                class="text-xs px-2 py-1 rounded-full font-medium">
+                {{ m.is_active ? '啟用' : '停用' }}
+              </span>
+            </td>
+            <td class="px-6 py-4 text-center">
+              <button @click="toggleActive(m)"
+                :class="m.is_active
+                  ? 'bg-red-50 text-red-600 hover:bg-red-100'
+                  : 'bg-green-50 text-green-700 hover:bg-green-100'"
+                class="text-xs px-3 py-1 rounded-lg transition">
+                {{ m.is_active ? '停用' : '啟用' }}
+              </button>
+            </td>
+          </tr>
+          <tr v-if="members.length === 0">
+            <td colspan="5" class="px-6 py-10 text-center text-slate-400">無符合的會員</td>
+          </tr>
+        </tbody>
+      </table>
+    </div>
+  </main>
+</template>