feat:實作 Member Portal MVP 前端與後端整合

後端：
- 新增 DivingOffer Model / DivingOfferController（列表+詳情 API，支援搜尋/篩選/分頁）
- 修正 Google OAuth callback 改為 redirect 至前端（SocialAuthController）
- 新增 config/cors.php 允許前端 origin
- .gitignore 新增 frontend/ 排除規則

前端（frontend/）：
- Vue 3 + Vite + Tailwind CSS + Pinia + Vue Router
- 頁面：首頁、課程列表、課程詳情、登入、註冊、個人資料、OAuth callback
- 整合至 Docker（multi-stage build，nginx 靜態服務於 port 5173）

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

frontend/src/router/index.js

@@ -0,0 +1,26 @@
+import { createRouter, createWebHistory } from 'vue-router'
+import { useAuthStore } from '../stores/auth'
+
+const routes = [
+  { path: '/',               component: () => import('../views/HomeView.vue') },
+  { path: '/courses',        component: () => import('../views/CoursesView.vue') },
+  { path: '/courses/:id',    component: () => import('../views/CourseDetailView.vue') },
+  { path: '/login',          component: () => import('../views/LoginView.vue') },
+  { path: '/register',       component: () => import('../views/RegisterView.vue') },
+  { path: '/auth/callback',  component: () => import('../views/AuthCallbackView.vue') },
+  { path: '/profile',        component: () => import('../views/ProfileView.vue'), meta: { requiresAuth: true } },
+]
+
+const router = createRouter({
+  history: createWebHistory(),
+  routes,
+})
+
+router.beforeEach((to) => {
+  const auth = useAuthStore()
+  if (to.meta.requiresAuth && !auth.isLoggedIn) {
+    return { path: '/login' }
+  }
+})
+
+export default router