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/components/NavBar.vue

@@ -0,0 +1,48 @@
+<script setup>
+import { useAuthStore } from '../stores/auth'
+import { useRouter } from 'vue-router'
+
+const auth   = useAuthStore()
+const router = useRouter()
+
+async function handleLogout() {
+  await auth.logout()
+  router.push('/login')
+}
+</script>
+
+<template>
+  <nav class="bg-ocean-800 text-white shadow-md">
+    <div class="max-w-6xl mx-auto px-4 h-16 flex items-center justify-between">
+      <RouterLink to="/" class="text-xl font-bold tracking-wide hover:text-ocean-100 transition">
+        🤿 CFDive
+      </RouterLink>
+
+      <div class="flex items-center gap-6 text-sm font-medium">
+        <RouterLink to="/courses" class="hover:text-ocean-100 transition">探索課程</RouterLink>
+
+        <template v-if="auth.isLoggedIn">
+          <span class="text-ocean-200 hidden sm:inline">
+            👤 {{ auth.user?.name }}
+          </span>
+          <RouterLink to="/profile" class="hover:text-ocean-100 transition">個人資料</RouterLink>
+          <button
+            @click="handleLogout"
+            class="bg-ocean-600 hover:bg-ocean-500 px-4 py-1.5 rounded-full transition"
+          >
+            登出
+          </button>
+        </template>
+        <template v-else>
+          <RouterLink to="/login"    class="hover:text-ocean-100 transition">登入</RouterLink>
+          <RouterLink
+            to="/register"
+            class="bg-ocean-600 hover:bg-ocean-500 px-4 py-1.5 rounded-full transition"
+          >
+            註冊
+          </RouterLink>
+        </template>
+      </div>
+    </div>
+  </nav>
+</template>