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/workspace/page.tsx

@@ -0,0 +1,20 @@
+import fs from "fs";
+import path from "path";
+
+import { redirect } from "next/navigation";
+
+import { env } from "@/env";
+
+export default function WorkspacePage() {
+  if (env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true") {
+    const firstThread = fs
+      .readdirSync(path.resolve(process.cwd(), "public/demo/threads"), {
+        withFileTypes: true,
+      })
+      .find((thread) => thread.isDirectory() && !thread.name.startsWith("."));
+    if (firstThread) {
+      return redirect(`/workspace/chats/${firstThread.name}`);
+    }
+  }
+  return redirect("/workspace/chats/new");
+}