feat: 实现关注系统 + 通知侧边栏分类 TAB + 点赞聚合通知

- 新增关注系统：UserFollow 模型、FollowService（toggle/status/列表隐私控制）
- User 新增 FollowersCount/FollowingCount/FollowListPublic/NotifyPrefs 字段
- Space 页面增加四态关注按钮（关注/已关注/回关/已互粉）+ 粉丝/关注数链接
- 新增 /space/:uid/followers 和 /space/:uid/following 列表页
- 新增 NotifyFollow/NotifyLikeAggregated 通知类型
- ReactionService 点赞时写入 daily_like_summary，访问时生成聚合通知
- FollowService 关注时触发 NotifyFollow 通知
- 消息中心侧边栏升级为分类 TAB（全部/系统通知/@艾特/点赞/关注）
- NotificationService 新增 ListByCategory 按分类分页查询

templates/MetaLab-2026/html/space/index.html

@@ -30,6 +30,15 @@
                     <span class="space-divider">·</span>
                     <span class="space-joined">加入于 {{.SpaceUser.CreatedAt.Format "2006-01-02"}}</span>
                 </div>
+                <div class="follow-links">
+                    <a href="/space/{{.SpaceUser.ID}}/following"><strong>{{.SpaceUser.FollowingCount}}</strong> 关注</a>
+                    <a href="/space/{{.SpaceUser.ID}}/followers"><strong>{{.SpaceUser.FollowersCount}}</strong> 粉丝</a>
+                </div>
+                {{if not .IsOwnSpace}}
+                <div class="follow-btn-wrapper">
+                    <button id="followBtn" class="follow-btn" data-uid="{{.SpaceUser.ID}}">关注</button>
+                </div>
+                {{end}}
             </div>
         </div>
     </div>
@@ -89,5 +98,75 @@
 {{template "layout/footer.html" .}}
 
 <script src="/static/js/common.js?v={{assetV "/static/js/common.js"}}"></script>
+{{if not .IsOwnSpace}}
+<script>
+(function() {
+    var followBtn = document.getElementById('followBtn');
+    if (!followBtn) return;
+    var targetUid = followBtn.getAttribute('data-uid');
+    var csrfMeta = document.querySelector('meta[name="csrf-token"]');
+    var csrfToken = csrfMeta ? csrfMeta.getAttribute('content') : '';
+
+    // 四个按钮状态文案
+    var labels = {
+        none: '关注',
+        following: '已关注',
+        followBack: '回关',
+        mutual: '已互粉'
+    };
+
+    var classes = {
+        none: '',
+        following: 'following',
+        followBack: '',
+        mutual: 'mutual'
+    };
+
+    function buttonState(status) {
+        if (status.i_follow && status.they_follow) return 'mutual';
+        if (status.i_follow) return 'following';
+        if (status.they_follow) return 'followBack';
+        return 'none';
+    }
+
+    function updateBtn(status) {
+        var state = buttonState(status);
+        followBtn.textContent = labels[state];
+        followBtn.className = 'follow-btn ' + (classes[state] || '');
+    }
+
+    // 获取初始状态
+    fetch('/api/users/' + targetUid + '/follow-status')
+        .then(function(res) { return res.json(); })
+        .then(function(data) {
+            if (data && data.success && data.data) {
+                updateBtn(data.data);
+            }
+        });
+
+    // 点击切换
+    followBtn.addEventListener('click', function() {
+        followBtn.classList.add('waiting');
+        var xhr = new XMLHttpRequest();
+        xhr.open('POST', '/api/users/' + targetUid + '/follow', true);
+        xhr.setRequestHeader('X-CSRF-Token', csrfToken);
+        xhr.onreadystatechange = function() {
+            if (xhr.readyState === 4) {
+                followBtn.classList.remove('waiting');
+                if (xhr.status === 200) {
+                    try {
+                        var resp = JSON.parse(xhr.responseText);
+                        if (resp.data && resp.data.status) {
+                            updateBtn(resp.data.status);
+                        }
+                    } catch(e) {}
+                }
+            }
+        };
+        xhr.send();
+    });
+})();
+</script>
+{{end}}
 </body>
 </html>