feat: 重构博客为水墨纸质风格 + 搭建后台管理系统

- 重新设计全站 UI：parchment/ink/terracotta 水墨纸质色系，宋式 serif 排版
- 新增页面：文章列表、文章详情、分类、标签、关于
- GSAP ScrollTrigger 滚动动画 + 逐字揭示效果
- 后台管理系统 /admin：文章/分类/标签 CRUD，JSON 文件存储
- 登录认证（cookie session）
- 设计系统文档 UI.md

src/app/api/posts/route.ts

@@ -0,0 +1,36 @@
+import { NextRequest, NextResponse } from "next/server";
+import { cookies } from "next/headers";
+import { getPosts, createPost, deletePost } from "@/lib/store";
+
+async function checkAuth(): Promise<boolean> {
+  const cookieStore = await cookies();
+  return cookieStore.get("admin_session")?.value === "authenticated";
+}
+
+export async function GET() {
+  if (!(await checkAuth())) {
+    return NextResponse.json({ error: "未授权" }, { status: 401 });
+  }
+  const posts = getPosts();
+  return NextResponse.json(posts);
+}
+
+export async function POST(request: NextRequest) {
+  if (!(await checkAuth())) {
+    return NextResponse.json({ error: "未授权" }, { status: 401 });
+  }
+  const body = await request.json();
+  const post = createPost(body);
+  return NextResponse.json(post, { status: 201 });
+}
+
+export async function DELETE(request: NextRequest) {
+  if (!(await checkAuth())) {
+    return NextResponse.json({ error: "未授权" }, { status: 401 });
+  }
+  const { searchParams } = new URL(request.url);
+  const id = searchParams.get("id");
+  if (!id) return NextResponse.json({ error: "缺少 id" }, { status: 400 });
+  const ok = deletePost(id);
+  return NextResponse.json({ ok });
+}