fix: 修复登录重定向失效 + 404页面友好化

- ShowPage 未登录用户看未发布帖子时引导登录（携带 redirect 参数），替代直接 404
- login.js 无 redirect 参数时回退到同站 Referer 页面
- 404 页面重设计：SVG 图标 + 中文提示 + 返回首页和浏览帖子双按钮
- posts.css 新增 404 页面按钮样式

internal/controller/post_controller.go

@@ -95,6 +95,11 @@ func (ctrl *PostController) ShowPage(c *gin.Context) {
 
 	// 仅 approved 公开可见（作者本人 + moderator+ 可预览其他状态）
 	if post.Status != model.PostStatusApproved && !ctrl.postService.IsPostAccessible(uid, role, post.UserID) {
+		// 未登录用户：引导登录后回到当前帖子
+		if uid == 0 {
+			common.RedirectToLogin(c)
+			return
+		}
 		c.HTML(http.StatusNotFound, "posts/404.html", common.BuildPageData(c, gin.H{
 			"Title": "未找到",
 		}))

templates/MetaLab-2026/html/posts/404.html

@@ -3,9 +3,17 @@
 {{template "layout/nav.html" .}}
 <div class="container">
     <div class="error-404">
-        <h1>404</h1>
-        <p>帖子不存在或已被删除</p>
-        <a href="/posts" class="btn btn-primary">返回帖子列表</a>
+        <div class="error-404-icon">
+            <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
+                <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>
+        </div>
+        <h1>页面未找到</h1>
+        <p>该帖子可能已被删除、尚未发布，或您输入的地址有误</p>
+        <div class="error-404-actions">
+            <a href="/" class="btn btn-secondary">返回首页</a>
+            <a href="/posts" class="btn btn-primary">浏览帖子</a>
+        </div>
     </div>
 </div>
 {{template "layout/footer.html" .}}

templates/MetaLab-2026/static/css/posts.css

@@ -200,19 +200,67 @@
 /* ========== 404 ========== */
 .error-404 {
     text-align: center;
-    padding: 80px 0;
+    padding: 100px 0;
+    max-width: 480px;
+    margin: 0 auto;
+}
+
+.error-404-icon {
+    color: #d1d5db;
+    margin-bottom: 24px;
+}
+
+.error-404-icon svg {
+    width: 72px;
+    height: 72px;
 }
 
 .error-404 h1 {
-    font-size: 72px;
-    color: #d1d5db;
-    margin: 0;
+    font-size: 24px;
+    color: #374151;
+    margin: 0 0 8px;
+    font-weight: 600;
 }
 
 .error-404 p {
-    font-size: 18px;
-    color: #6b7280;
-    margin: 12px 0 24px;
+    font-size: 15px;
+    color: #9ca3af;
+    margin: 0 0 32px;
+    line-height: 1.6;
+}
+
+.error-404-actions {
+    display: flex;
+    justify-content: center;
+    gap: 12px;
+}
+
+.error-404-actions .btn {
+    padding: 10px 24px;
+    border-radius: 8px;
+    font-size: 14px;
+    text-decoration: none;
+    transition: all 0.2s;
+}
+
+.error-404-actions .btn-primary {
+    background: #2563eb;
+    color: #fff;
+    border: none;
+}
+
+.error-404-actions .btn-primary:hover {
+    background: #1d4ed8;
+}
+
+.error-404-actions .btn-secondary {
+    background: #f3f4f6;
+    color: #374151;
+    border: 1px solid #e5e7eb;
+}
+
+.error-404-actions .btn-secondary:hover {
+    background: #e5e7eb;
 }
 
 /* ========== 空状态 ========== */

templates/MetaLab-2026/static/js/login.js

@@ -19,6 +19,19 @@
     function getRedirect() {
         var m = window.location.search.match(/[?&]redirect=([^&]+)/);
         if (m) return decodeURIComponent(m[1]);
+        // 回退：如果来源页是本站页面，跳回来源页
+        try {
+            var ref = document.referrer;
+            if (ref) {
+                var a = document.createElement('a');
+                a.href = ref;
+                if (a.hostname === window.location.hostname &&
+                    a.pathname !== window.location.pathname &&
+                    a.pathname.indexOf('/auth/') !== 0) {
+                    return a.pathname + a.search + a.hash;
+                }
+            }
+        } catch (e) {}
         return '/';
     }