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/app/settings/ProfileForm.tsx

@@ -0,0 +1,145 @@
+"use client";
+
+import { useState } from "react";
+import { useRouter } from "next/navigation";
+import { apiUpdateProfile, type User } from "@/lib/api";
+
+interface ProfileFormProps {
+  user: User;
+}
+
+/**
+ * 个人资料编辑表单：昵称、头像 URL、邮箱、签名。
+ * 提交成功后刷新 layout 使 Header 同步最新昵称/头像，并在页面内显示成功提示。
+ */
+export default function ProfileForm({ user }: ProfileFormProps) {
+  const router = useRouter();
+  const [nickname, setNickname] = useState(user.nickname || "");
+  const [avatar, setAvatar] = useState(user.avatar || "");
+  const [email, setEmail] = useState(user.email || "");
+  const [signature, setSignature] = useState(user.signature || "");
+  const [submitting, setSubmitting] = useState(false);
+  const [error, setError] = useState("");
+  const [success, setSuccess] = useState("");
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    setError("");
+    setSuccess("");
+
+    const trimmed = nickname.trim();
+    if (!trimmed) {
+      setError("昵称不能为空");
+      return;
+    }
+    if (trimmed.length > 64) {
+      setError("昵称不能超过 64 个字符");
+      return;
+    }
+    if (signature.length > 255) {
+      setError("签名不能超过 255 个字符");
+      return;
+    }
+
+    setSubmitting(true);
+    try {
+      const res = await apiUpdateProfile({
+        nickname: trimmed,
+        avatar: avatar.trim(),
+        email: email.trim(),
+        signature,
+      });
+      if (res.user) {
+        setSuccess("资料已保存");
+        // 刷新 layout 让 Header 同步最新昵称/头像
+        router.refresh();
+      } else {
+        setError(res.error || "保存失败");
+      }
+    } catch {
+      setError("网络错误，请重试");
+    } finally {
+      setSubmitting(false);
+    }
+  };
+
+  return (
+    <>
+      <p className="font-bold text-[15px] mb-3.5" style={{ color: "var(--ink)" }}>
+        个人资料
+      </p>
+
+      <form onSubmit={handleSubmit} className="panel p-5 sm:p-6 space-y-5">
+        {success && <div className="alert-ok" role="status">{success}</div>}
+        {error && <div className="alert-error" role="alert">{error}</div>}
+
+        <div>
+          <label className="field-label" htmlFor="pf-nickname">昵称</label>
+          <input
+            id="pf-nickname"
+            type="text"
+            value={nickname}
+            onChange={(e) => setNickname(e.target.value)}
+            required
+            maxLength={64}
+            className="field"
+            placeholder="请输入昵称"
+          />
+        </div>
+
+        <div>
+          <label className="field-label" htmlFor="pf-avatar">头像链接</label>
+          <input
+            id="pf-avatar"
+            type="url"
+            value={avatar}
+            onChange={(e) => setAvatar(e.target.value)}
+            maxLength={512}
+            className="field"
+            placeholder="https://example.com/avatar.png"
+          />
+          <p className="meta mt-2">填写图片 URL，留空则使用默认字母头像</p>
+        </div>
+
+        <div>
+          <label className="field-label" htmlFor="pf-email">邮箱</label>
+          <input
+            id="pf-email"
+            type="email"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+            maxLength={128}
+            className="field"
+            placeholder="your@email.com"
+          />
+        </div>
+
+        <div>
+          <label className="field-label" htmlFor="pf-signature">
+            个性签名
+            <span className="font-normal ml-1.5" style={{ color: "var(--ink-3)" }}>
+              ({signature.length}/255)
+            </span>
+          </label>
+          <textarea
+            id="pf-signature"
+            value={signature}
+            onChange={(e) => setSignature(e.target.value)}
+            maxLength={255}
+            rows={3}
+            className="field"
+            placeholder="介绍一下自己吧"
+          />
+        </div>
+
+        <button
+          type="submit"
+          disabled={submitting}
+          className="btn btn-primary w-full justify-center mt-1"
+        >
+          {submitting ? "保存中..." : "保存资料"}
+        </button>
+      </form>
+    </>
+  );
+}