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/messages/index.html

@@ -10,13 +10,29 @@
             <h2>消息中心</h2>
         </div>
         <nav class="msg-sidebar-nav">
-            <span class="msg-sidebar-item active">
+            <a href="/messages?tab=all" class="msg-sidebar-item{{if or (eq .CurrentTab "all") (eq .CurrentTab "")}} active{{end}}">
                 <svg class="msg-sidebar-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9"/><path d="M13.73 21a2 2 0 0 1-3.46 0"/></svg>
                 全部消息
                 {{if .UnreadCount}}
                 <span class="msg-sidebar-count">{{.UnreadCount}}</span>
                 {{end}}
-            </span>
+            </a>
+            <a href="/messages?tab=system" class="msg-sidebar-item{{if eq .CurrentTab "system"}} active{{end}}">
+                <svg class="msg-sidebar-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><circle cx="12" cy="12" r="10"/><line x1="12" y1="8" x2="12" y2="12"/><line x1="12" y1="16" x2="12.01" y2="16"/></svg>
+                系统通知
+            </a>
+            <a href="/messages?tab=mention" class="msg-sidebar-item{{if eq .CurrentTab "mention"}} active{{end}}">
+                <svg class="msg-sidebar-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M20 21v-2a4 4 0 0 0-4-4H8a4 4 0 0 0-4 4v2"/><circle cx="12" cy="7" r="4"/></svg>
+                @艾特我的
+            </a>
+            <a href="/messages?tab=like" class="msg-sidebar-item{{if eq .CurrentTab "like"}} active{{end}}">
+                <svg class="msg-sidebar-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M20.84 4.61a5.5 5.5 0 0 0-7.78 0L12 5.67l-1.06-1.06a5.5 5.5 0 0 0-7.78 7.78l1.06 1.06L12 21.23l7.78-7.78 1.06-1.06a5.5 5.5 0 0 0 0-7.78z"/></svg>
+                点赞通知
+            </a>
+            <a href="/messages?tab=follow" class="msg-sidebar-item{{if eq .CurrentTab "follow"}} active{{end}}">
+                <svg class="msg-sidebar-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M16 21v-2a4 4 0 0 0-4-4H5a4 4 0 0 0-4 4v2"/><circle cx="8.5" cy="7" r="4"/><line x1="20" y1="8" x2="20" y2="14"/><line x1="23" y1="11" x2="17" y2="11"/></svg>
+                关注通知
+            </a>
         </nav>
     </aside>
 
@@ -78,13 +94,13 @@
         {{if .TotalPages}}
         <div class="msg-pagination">
             {{if .HasPrev}}
-            <a href="/messages?page={{.PrevPage}}" class="msg-page-btn">上一页</a>
+            <a href="/messages?tab={{.CurrentTab}}&page={{.PrevPage}}" class="msg-page-btn">上一页</a>
             {{else}}
             <span class="msg-page-btn disabled">上一页</span>
             {{end}}
             <span class="msg-page-info">{{.Page}} / {{.TotalPages}}</span>
             {{if .HasNext}}
-            <a href="/messages?page={{.NextPage}}" class="msg-page-btn">下一页</a>
+            <a href="/messages?tab={{.CurrentTab}}&page={{.NextPage}}" class="msg-page-btn">下一页</a>
             {{else}}
             <span class="msg-page-btn disabled">下一页</span>
             {{end}}