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/stores/auth.js

@@ -0,0 +1,38 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import api from '../api/axios'
+
+export const useAuthStore = defineStore('auth', () => {
+  const user  = ref(null)
+  const token = ref(null)
+
+  const isLoggedIn = computed(() => !!token.value)
+
+  function init() {
+    const saved = localStorage.getItem('token')
+    const savedUser = localStorage.getItem('user')
+    if (saved) {
+      token.value = saved
+      user.value  = savedUser ? JSON.parse(savedUser) : null
+    }
+  }
+
+  function setAuth(userData, tokenValue) {
+    user.value  = userData
+    token.value = tokenValue
+    localStorage.setItem('token', tokenValue)
+    localStorage.setItem('user', JSON.stringify(userData))
+  }
+
+  async function logout() {
+    try {
+      await api.post('/member/logout')
+    } catch {}
+    user.value  = null
+    token.value = null
+    localStorage.removeItem('token')
+    localStorage.removeItem('user')
+  }
+
+  return { user, token, isLoggedIn, init, setAuth, logout }
+})