fix: 锁定机制不再改变帖子状态，锁定与退回独立

- Post 模型新增 IsLocked 字段，与 Status 解耦
- Lock 仅设 IsLocked=true（不改 Status），已通过帖子锁定后仍公开可见
- Unlock 仅设 IsLocked=false（不改 Status）
- Update/EditPage 编辑检查改用 IsLocked 而非 Status==locked
- Reject 与 Lock 独立，可单独退回或锁定+退回组合使用
- 新增 ErrPostCannotLock 错误哨兵
- 前端模板编辑按钮/锁定标识基于 IsLocked 渲染

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

@@ -13,6 +13,9 @@
                 {{if ne .Post.Status "approved"}}
                 <span class="post-status post-status-{{.Post.Status}}">{{index $.StatusNames .Post.Status}}</span>
                 {{end}}
+                {{if .Post.IsLocked}}
+                <span class="post-status post-status-locked">已锁定</span>
+                {{end}}
             </div>
         </header>
 
@@ -27,7 +30,7 @@
 
     {{if .IsLoggedIn}}
     <div class="post-actions">
-        {{if and $.Post (or (eq $.Post.UserID $.UID) $.CanAccessAdmin) (ne $.Post.Status "pending") (ne $.Post.Status "locked")}}
+        {{if and $.Post (or (eq $.Post.UserID $.UID) $.CanAccessAdmin) (ne $.Post.Status "pending") (not $.Post.IsLocked)}}
         <a href="/posts/{{$.Post.ID}}/edit" class="btn btn-secondary">编辑</a>
         {{end}}
         {{if and $.Post (eq $.Post.UserID $.UID) (or (eq $.Post.Status "draft") (eq $.Post.Status "rejected"))}}

templates/admin/html/posts/index.html

@@ -13,7 +13,6 @@
                     <option value="pending" {{if eq .Status "pending"}}selected{{end}}>待审核</option>
                     <option value="approved" {{if eq .Status "approved"}}selected{{end}}>已发布</option>
                     <option value="rejected" {{if eq .Status "rejected"}}selected{{end}}>已退回</option>
-                    <option value="locked" {{if eq .Status "locked"}}selected{{end}}>已锁定</option>
                 </select>
                 <button type="submit" class="btn btn-primary">搜索</button>
             </form>
@@ -43,7 +42,7 @@
                     <td>{{.ID}}</td>
                     <td><a href="/posts/{{.ID}}" target="_blank" class="post-link">{{.Title}}</a></td>
                     <td>{{if .AuthorName}}{{.AuthorName}}({{.UserID}}){{else}}UID{{.UserID}}{{end}}</td>
-                    <td><span class="status-badge status-{{.Status}}">{{index $.StatusNames .Status}}</span></td>
+                    <td><span class="status-badge status-{{.Status}}">{{index $.StatusNames .Status}}</span>{{if .IsLocked}} <span class="status-badge status-locked">已锁定</span>{{end}}</td>
                     <td>{{.CreatedAt.Format "2006-01-02 15:04"}}</td>
                     <td class="actions-cell">
                         <div class="action-btns">
@@ -54,10 +53,10 @@
                             {{if eq .Status "approved"}}
                             <button class="btn btn-sm btn-warning post-reject" data-id="{{.ID}}">退回</button>
                             {{end}}
-                            {{if and (ne .Status "locked") (ne .Status "pending")}}
+                            {{if and (not .IsLocked) (ne .Status "pending")}}
                             <button class="btn btn-sm btn-danger post-lock" data-id="{{.ID}}">锁定</button>
                             {{end}}
-                            {{if eq .Status "locked"}}
+                            {{if .IsLocked}}
                             <button class="btn btn-sm btn-success post-unlock" data-id="{{.ID}}">解锁</button>
                             {{end}}
                         </div>