Initial commit: hardened DeerFlow factory

Vendored deer-flow upstream (bytedance/deer-flow) plus prompt-injection
hardening:

- New deerflow.security package: content_delimiter, html_cleaner,
  sanitizer (8 layers — invisible chars, control chars, symbols, NFC,
  PUA, tag chars, horizontal whitespace collapse with newline/tab
  preservation, length cap)
- New deerflow.community.searx package: web_search, web_fetch,
  image_search backed by a private SearX instance, every external
  string sanitized and wrapped in <<<EXTERNAL_UNTRUSTED_CONTENT>>>
  delimiters
- All native community web providers (ddg_search, tavily, exa,
  firecrawl, jina_ai, infoquest, image_search) replaced with hard-fail
  stubs that raise NativeWebToolDisabledError at import time, so a
  misconfigured tool.use path fails loud rather than silently falling
  back to unsanitized output
- Native client back-doors (jina_client.py, infoquest_client.py)
  stubbed too
- Native-tool tests quarantined under tests/_disabled_native/
  (collect_ignore_glob via local conftest.py)
- Sanitizer Layer 7 fix: only collapse horizontal whitespace, preserve
  newlines and tabs so list/table structure survives
- Hardened runtime config.yaml references only the searx-backed tools
- Factory overlay (backend/) kept in sync with deer-flow tree as a
  reference / source

See HARDENING.md for the full audit trail and verification steps.

deer-flow/frontend/src/app/[lang]/docs/layout.tsx

@@ -0,0 +1,51 @@
+import type { PageMapItem } from "nextra";
+import { getPageMap } from "nextra/page-map";
+import { Layout } from "nextra-theme-docs";
+
+import { Footer } from "@/components/landing/footer";
+import { Header } from "@/components/landing/header";
+import { getLocaleByLang } from "@/core/i18n/locale";
+import "nextra-theme-docs/style.css";
+
+const i18n = [
+  { locale: "en", name: "English" },
+  { locale: "zh", name: "中文" },
+];
+
+function formatPageRoute(base: string, items: PageMapItem[]): PageMapItem[] {
+  return items.map((item) => {
+    if ("route" in item && !item.route.startsWith(base)) {
+      item.route = `${base}${item.route}`;
+    }
+    if ("children" in item && item.children) {
+      item.children = formatPageRoute(base, item.children);
+    }
+    return item;
+  });
+}
+
+export default async function DocLayout({ children, params }) {
+  const { lang } = await params;
+  const locale = getLocaleByLang(lang);
+  const pages = await getPageMap(`/${lang}`);
+  const pageMap = formatPageRoute(`/${lang}/docs`, pages);
+
+  return (
+    <Layout
+      navbar={
+        <Header
+          className="relative max-w-full px-10"
+          homeURL="/"
+          locale={locale}
+        />
+      }
+      pageMap={pageMap}
+      docsRepositoryBase="https://github.com/bytedance/deerflow/tree/main/frontend/src/content"
+      footer={<Footer />}
+      i18n={i18n}
+      // ... Your additional layout options
+    >
+      {children}
+    </Layout>
+  );
+}