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/Header.tsx

@@ -19,9 +19,8 @@ import {
   User as UserIcon,
   ChevronDown,
   Megaphone,
-  Layers,
 } from "lucide-react";
-import { apiLogout, apiMe, type User, type Board } from "@/lib/api";
+import { apiLogout, apiMe, type User } from "@/lib/api";
 import { hasAuthCookieHint } from "@/lib/cookies";
 import NotificationBell from "./NotificationBell";
 import Avatar from "./Avatar";
@@ -30,12 +29,10 @@ export default function Header({
   initialUser,
   initialUnread = 0,
   initialTheme = "light",
-  boards = [],
 }: {
   initialUser: User | null;
   initialUnread?: number;
   initialTheme?: "light" | "dark";
-  boards?: Board[];
 }) {
   const router = useRouter();
   const pathname = usePathname();
@@ -171,7 +168,6 @@ export default function Header({
             <NavPill href="/" active={pathname === "/"} icon={<Home size={14} />}>
               首页
             </NavPill>
-            <BoardsMenu boards={boards} />
           </nav>
         </div>
 
@@ -285,39 +281,6 @@ export default function Header({
             {!user && <MobileLink href="/login">登录</MobileLink>}
             {!user && <MobileLink href="/register">注册</MobileLink>}
           </div>
-          {/* 全站板块入口：手机用户在任意页面都能切板块，不必回首页 */}
-          {boards.length > 0 && (
-            <div className="mt-3 pt-3 border-t" style={{ borderColor: "var(--line)" }}>
-              <p className="px-3 mb-1.5 text-[11.5px] font-bold tracking-[0.08em] uppercase" style={{ color: "var(--ink-3)" }}>
-                板块
-              </p>
-              <div className="grid grid-cols-2 gap-1">
-                {boards.map((b, i) => {
-                  const active = pathname === `/board/${b.id}`;
-                  return (
-                    <Link
-                      key={b.id}
-                      href={`/board/${b.id}`}
-                      onClick={() => setMenuOpen(false)}
-                      aria-current={active ? "page" : undefined}
-                      className="flex items-center gap-2 px-3 py-2.5 rounded-xl text-[13.5px] font-semibold transition-colors"
-                      style={{
-                        color: active ? "var(--accent)" : "var(--ink)",
-                        background: active ? "var(--accent-soft)" : "transparent",
-                      }}
-                    >
-                      <span
-                        className={`av-${Math.max(0, b.color_index ?? i) % 8} w-6 h-6 rounded-lg flex items-center justify-center text-[11px] font-bold shrink-0`}
-                      >
-                        {b.name.slice(0, 1)}
-                      </span>
-                      <span className="truncate">{b.name}</span>
-                    </Link>
-                  );
-                })}
-              </div>
-            </div>
-          )}
           <div className="pt-3 mt-2 border-t flex items-center justify-between" style={{ borderColor: "var(--line)" }}>
             <button onClick={toggleTheme} className="btn btn-line btn-sm">
               {theme === "dark" ? <Sun size={14} /> : <Moon size={14} />}
@@ -362,96 +325,6 @@ function NavPill({
   );
 }
 
-/**
- * 板块下拉菜单（桌面端）：全站任意页面的 Header 都能直达板块，
- * 替代原先只有首页左栏才有板块导航的布局局限
- */
-function BoardsMenu({ boards }: { boards: Board[] }) {
-  const pathname = usePathname();
-  const [open, setOpen] = useState(false);
-  const menuRef = useRef<HTMLDivElement>(null);
-
-  useEffect(() => {
-    if (!open) return;
-    const onDown = (e: MouseEvent) => {
-      if (menuRef.current && !menuRef.current.contains(e.target as Node)) setOpen(false);
-    };
-    const onKey = (e: KeyboardEvent) => {
-      if (e.key === "Escape") setOpen(false);
-    };
-    document.addEventListener("mousedown", onDown);
-    document.addEventListener("keydown", onKey);
-    return () => {
-      document.removeEventListener("mousedown", onDown);
-      document.removeEventListener("keydown", onKey);
-    };
-  }, [open]);
-
-  if (boards.length === 0) return null;
-  const active = pathname.startsWith("/board/");
-
-  return (
-    <div className="relative" ref={menuRef}>
-      <button
-        onClick={() => setOpen((v) => !v)}
-        aria-haspopup="menu"
-        aria-expanded={open}
-        className="inline-flex items-center gap-1.5 px-3.5 py-2 rounded-full text-[13.5px] font-semibold transition-colors"
-        style={
-          active || open
-            ? { background: "var(--accent-soft)", color: "var(--accent)" }
-            : { color: "var(--ink-2)" }
-        }
-      >
-        <Layers size={14} />
-        板块
-        <ChevronDown
-          size={12}
-          className="transition-transform duration-200"
-          style={{ transform: open ? "rotate(180deg)" : "none" }}
-        />
-      </button>
-
-      {open && (
-        <div
-          role="menu"
-          className="absolute left-0 mt-2.5 w-60 max-h-[60vh] overflow-y-auto p-1.5 z-50 j13-toast-in"
-          style={{
-            background: "var(--panel)",
-            border: "1px solid var(--line)",
-            borderRadius: "var(--r)",
-            boxShadow: "var(--shadow-lg)",
-          }}
-        >
-          {boards.map((b, i) => {
-            const isActive = pathname === `/board/${b.id}`;
-            return (
-              <Link
-                key={b.id}
-                href={`/board/${b.id}`}
-                onClick={() => setOpen(false)}
-                role="menuitem"
-                className="flex items-center gap-2.5 px-3 py-2.5 rounded-xl text-[13.5px] font-semibold transition-colors hover:bg-[var(--panel-2)]"
-                style={{
-                  color: isActive ? "var(--accent)" : "var(--ink)",
-                  background: isActive ? "var(--nav-active-bg)" : undefined,
-                }}
-              >
-                <span
-                  className={`av-${Math.max(0, b.color_index ?? i) % 8} w-7 h-7 rounded-lg flex items-center justify-center text-[12px] font-bold shrink-0`}
-                >
-                  {b.name.slice(0, 1)}
-                </span>
-                <span className="flex-1 truncate">{b.name}</span>
-              </Link>
-            );
-          })}
-        </div>
-      )}
-    </div>
-  );
-}
-
 function MobileLink({
   href,
   active,