feat: 实现赞/踩系统（P2）

- 新增 PostLike/PostDislike 模型，复合主键 (user_id, post_id)
- Post 表新增 LikesCount/DislikesCount 冗余计数器
- Repository 层：reaction_repo.go，含 WithTx 事务支持
- Service 层：reaction_service.go，赞踩互斥逻辑（6 态切换），事务包裹
- Controller 层：reaction_controller.go，3 个 API（ToggleLike/ToggleDislike/GetReaction）
- 接口定义：controller/interfaces.go 新增 reactionUseCase，service/repository.go 新增 ReactionStore
- 路由注册 + 依赖注入 + AutoMigrate
- 前端：文章详情页赞踩按钮 + 状态查询 + 401 跳转登录
- 样式：posts.css 新增赞踩按钮样式

templates/MetaLab-2026/html/posts/show.html

@@ -31,6 +31,17 @@
         <div class="post-detail-body" id="postContent"></div>
     </article>
 
+    <!-- 赞/踩按钮 -->
+    <div class="post-reactions" id="postReactions" data-post-id="{{.Post.ID}}">
+        <button class="reaction-btn reaction-like-btn" id="likeBtn" title="点赞">
+            <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" width="20" height="20"><path d="M14 9V5a3 3 0 0 0-3-3l-4 9v11h11.28a2 2 0 0 0 2-1.7l1.38-9a2 2 0 0 0-2-2.3H14zM7 22H4a2 2 0 0 1-2-2v-7a2 2 0 0 1 2-2h3"/></svg>
+            <span class="reaction-like-count" id="likesCount">{{.Post.LikesCount}}</span>
+        </button>
+        <button class="reaction-btn reaction-dislike-btn" id="dislikeBtn" title="踩">
+            <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" width="20" height="20"><path d="M10 15v4a3 3 0 0 0 3 3l4-9V2H5.72a2 2 0 0 0-2 1.7l-1.38 9a2 2 0 0 0 2 2.3H10zM17 2h2.67A2.31 2.31 0 0 1 22 4v7a2.31 2.31 0 0 1-2.33 2H17"/></svg>
+        </button>
+    </div>
+
     {{if .IsLoggedIn}}
     <div class="post-actions">
         {{if and $.Post (or (eq $.Post.UserID $.UID) $.CanAccessAdmin) (ne $.Post.Status "pending") (not $.Post.IsLocked)}}
@@ -253,6 +264,82 @@
 })();
 </script>
 
+<script>
+// ========== 赞/踩系统 ==========
+(function() {
+    var container = document.getElementById('postReactions');
+    var likeBtn = document.getElementById('likeBtn');
+    var dislikeBtn = document.getElementById('dislikeBtn');
+    var likesCountEl = document.getElementById('likesCount');
+    if (!container || !likeBtn || !dislikeBtn) return;
+
+    var postId = container.dataset.postId;
+    var csrfMeta = document.querySelector('meta[name="csrf-token"]');
+    var csrfToken = csrfMeta ? csrfMeta.getAttribute('content') : '';
+
+    // 页面加载时获取当前反应状态
+    fetch('/api/posts/' + postId + '/reaction')
+        .then(function(r) { return r.json(); })
+        .then(function(d) {
+            if (!d.success || !d.data) return;
+            updateUI(d.data.reaction, d.data.likes_count);
+        })
+        .catch(function() {});
+
+    function updateUI(reaction, count) {
+        likeBtn.classList.remove('active');
+        dislikeBtn.classList.remove('active');
+        if (reaction === 'liked') likeBtn.classList.add('active');
+        if (reaction === 'disliked') dislikeBtn.classList.add('active');
+        if (typeof count === 'number') likesCountEl.textContent = count;
+    }
+
+    likeBtn.addEventListener('click', function() {
+        likeBtn.disabled = true;
+        fetch('/api/posts/' + postId + '/like', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': csrfToken }
+        })
+        .then(function(r) {
+            if (r.status === 401) { window.location.href = '/login?redirect=/posts/' + postId; return null; }
+            return r.json();
+        })
+        .then(function(d) {
+            likeBtn.disabled = false;
+            if (!d) return;
+            if (d.success) {
+                updateUI(d.data.liked ? 'liked' : 'none', d.data.likes_count);
+            } else {
+                alert(d.message || '操作失败');
+            }
+        })
+        .catch(function() { likeBtn.disabled = false; });
+    });
+
+    dislikeBtn.addEventListener('click', function() {
+        dislikeBtn.disabled = true;
+        fetch('/api/posts/' + postId + '/dislike', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': csrfToken }
+        })
+        .then(function(r) {
+            if (r.status === 401) { window.location.href = '/login?redirect=/posts/' + postId; return null; }
+            return r.json();
+        })
+        .then(function(d) {
+            dislikeBtn.disabled = false;
+            if (!d) return;
+            if (d.success) {
+                updateUI(d.data.disliked ? 'disliked' : 'none');
+            } else {
+                alert(d.message || '操作失败');
+            }
+        })
+        .catch(function() { dislikeBtn.disabled = false; });
+    });
+})();
+</script>
+
 <script>
 // ========== 评论系统 ==========
 (function() {