feat(site): add self-contained static 404 page

docs/app/not-found.tsx

@@ -0,0 +1,52 @@
+// Self-contained static 404: the top-level not-found has no root layout in this
+// app (multiple root-layout groups), so global.css is not guaranteed to load —
+// especially in `next dev`. Keep all styling inline and use zero client JS.
+const button = {
+  display: "inline-flex",
+  height: "40px",
+  alignItems: "center",
+  padding: "0 18px",
+  borderRadius: "8px",
+  fontSize: "13px",
+  fontWeight: 650,
+  textDecoration: "none",
+} as const;
+
+export default function NotFound() {
+  return (
+    <main
+      style={{
+        minHeight: "100vh",
+        display: "flex",
+        alignItems: "center",
+        justifyContent: "center",
+        background: "#08080a",
+        color: "#ededf0",
+        fontFamily: '-apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif',
+        textAlign: "center",
+        padding: "24px",
+        margin: 0,
+      }}
+    >
+      {/* No root layout on this route, so global.css may be absent (next dev):
+          reset the default body margin/background inline instead. */}
+      <style dangerouslySetInnerHTML={{ __html: "html,body{margin:0;padding:0;background:#08080a}" }} />
+      <div>
+        <p style={{ margin: 0, fontSize: "clamp(72px, 14vw, 140px)", fontWeight: 800, lineHeight: 1, letterSpacing: "-0.03em" }}>404</p>
+        <h1 style={{ margin: "18px 0 8px", fontSize: 21, fontWeight: 720 }}>页面不存在</h1>
+        <p style={{ margin: 0, fontSize: 14, lineHeight: 1.7, color: "#9c9ea3" }}>Page not found — 这个链接指向的页面不存在或已被移动。</p>
+        <div style={{ marginTop: 28, display: "flex", flexWrap: "wrap", justifyContent: "center", gap: 12 }}>
+          <a href="/cn" style={{ ...button, background: "#f0f1f4", color: "#0a0b0e" }}>
+            返回首页
+          </a>
+          <a href="/cn/plugins" style={{ ...button, border: "1px solid rgba(173,176,182,0.3)", color: "#9c9ea3" }}>
+            插件中心
+          </a>
+          <a href="/cn/docs/what-is-dbx" style={{ ...button, border: "1px solid rgba(173,176,182,0.3)", color: "#9c9ea3" }}>
+            文档
+          </a>
+        </div>
+      </div>
+    </main>
+  );
+}

docs/wrangler.json

@@ -4,7 +4,8 @@
   "main": "./worker.ts",
   "assets": {
     "directory": "./out",
-    "binding": "ASSETS"
+    "binding": "ASSETS",
+    "not_found_handling": "404-page"
   },
   "r2_buckets": [
     {