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/next.config.js

@@ -0,0 +1,61 @@
+/**
+ * Run `build` or `dev` with `SKIP_ENV_VALIDATION` to skip env validation. This is especially useful
+ * for Docker builds.
+ */
+import "./src/env.js";
+
+function getInternalServiceURL(envKey, fallbackURL) {
+  const configured = process.env[envKey]?.trim();
+  return configured && configured.length > 0
+    ? configured.replace(/\/+$/, "")
+    : fallbackURL;
+}
+import nextra from "nextra";
+
+const withNextra = nextra({});
+
+/** @type {import("next").NextConfig} */
+const config = {
+  i18n: {
+    locales: ["en", "zh"],
+    defaultLocale: "en",
+  },
+  devIndicators: false,
+  async rewrites() {
+    const rewrites = [];
+    const langgraphURL = getInternalServiceURL(
+      "DEER_FLOW_INTERNAL_LANGGRAPH_BASE_URL",
+      "http://127.0.0.1:2024",
+    );
+    const gatewayURL = getInternalServiceURL(
+      "DEER_FLOW_INTERNAL_GATEWAY_BASE_URL",
+      "http://127.0.0.1:8001",
+    );
+
+    if (!process.env.NEXT_PUBLIC_LANGGRAPH_BASE_URL) {
+      rewrites.push({
+        source: "/api/langgraph",
+        destination: langgraphURL,
+      });
+      rewrites.push({
+        source: "/api/langgraph/:path*",
+        destination: `${langgraphURL}/:path*`,
+      });
+    }
+
+    if (!process.env.NEXT_PUBLIC_BACKEND_BASE_URL) {
+      rewrites.push({
+        source: "/api/agents",
+        destination: `${gatewayURL}/api/agents`,
+      });
+      rewrites.push({
+        source: "/api/agents/:path*",
+        destination: `${gatewayURL}/api/agents/:path*`,
+      });
+    }
+
+    return rewrites;
+  },
+};
+
+export default withNextra(config);