feat: 添加用户个人资料编辑功能，优化页面布局与导航

1. 后端新增用户资料更新接口，支持修改昵称、头像、邮箱和签名
2. 前端新增资料编辑表单页面，适配响应式布局
3. 优化帖子详情页布局与移动端适配逻辑
4. 重构首页侧边栏导航，使用卡片式板块展示
5. 移除全局板块缓存，调整Header导航移除板块菜单
6. 补充用户签名展示功能，完善用户信息返回字段

frontend/components/home/WorkspaceNav.tsx

@@ -23,35 +23,64 @@ export function WorkspaceNav({ boards, user }: { boards: BoardWithCount[]; user:
           <PenSquare size={16} /> 发起讨论
         </Link>
 
+        {/* 「全部讨论」是重置筛选的动作入口，与板块目录分区展示 */}
+        <div className="space-y-0.5">
+          <Link
+            href="/"
+            className="j13-raillink"
+            aria-current={activeBoard === 0 ? "page" : undefined}
+          >
+            <Home size={16} className="shrink-0" />
+            <span className="flex-1 truncate">全部讨论</span>
+          </Link>
+        </div>
+
+        {/* 板块目录：发现型入口（介绍 + 讨论量），区别于帖子页面包屑的位置指引；
+            点击不离开工作台，仅在中栏筛选该板块帖子流 */}
         <div>
-          <p className="px-2.5 mb-1.5 text-[11.5px] font-bold tracking-[0.08em] uppercase" style={{ color: "var(--ink-3)" }}>
-            板块
+          <p
+            className="px-1 mb-2 flex items-center justify-between text-[11.5px] font-bold tracking-[0.08em] uppercase"
+            style={{ color: "var(--ink-3)" }}
+          >
+            <span>板块目录</span>
+            {boards.length > 0 && (
+              <span className="tracking-normal font-semibold tabular-nums">{boards.length} 个</span>
+            )}
           </p>
-          <div className="space-y-0.5">
-            <Link
-              href="/"
-              className="j13-raillink"
-              aria-current={activeBoard === 0 ? "page" : undefined}
-            >
-              <Home size={16} className="shrink-0" />
-              <span className="flex-1 truncate">全部讨论</span>
-            </Link>
-            {boards.map((b, i) => (
-              <Link
-                key={b.id}
-                href={boardHref(b.id)}
-                className="j13-raillink"
-                aria-current={activeBoard === b.id ? "page" : undefined}
-              >
-                <span
-                  className={`av-${i % 8} w-7 h-7 rounded-lg flex items-center justify-center text-[12px] font-bold shrink-0`}
+          <div className="space-y-2">
+            {boards.map((b, i) => {
+              const desc = b.description?.trim();
+              return (
+                <Link
+                  key={b.id}
+                  href={boardHref(b.id)}
+                  className="j13-bcard"
+                  aria-current={activeBoard === b.id ? "page" : undefined}
+                  aria-label={`${b.name}板块，${b.post_count} 篇讨论`}
                 >
-                  {b.name.slice(0, 1)}
-                </span>
-                <span className="flex-1 truncate">{b.name}</span>
-                <span className="meta text-[11.5px]">{b.post_count}</span>
-              </Link>
-            ))}
+                  <span
+                    className={`av-${i % 8} j13-bcard-ico`}
+                    aria-hidden="true"
+                  >
+                    {b.name.slice(0, 1)}
+                  </span>
+                  <span className="min-w-0 flex-1">
+                    <span className="flex items-center justify-between gap-2">
+                      <span
+                        className="truncate text-[13px] font-bold"
+                        style={{ color: "var(--ink)" }}
+                      >
+                        {b.name}
+                      </span>
+                      <span className="meta shrink-0 text-[11px] tabular-nums">
+                        {b.post_count} 篇
+                      </span>
+                    </span>
+                    {desc && <span className="j13-bcard-desc">{desc}</span>}
+                  </span>
+                </Link>
+              );
+            })}
           </div>
         </div>
       </div>