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/backend/packages/harness/deerflow/security/content_delimiter.py

@@ -0,0 +1,44 @@
+"""Content delimiter wrapper for safe LLM prompt integration."""
+
+from typing import Union
+import json
+
+
+# OpenClaw-style delimiters
+START_DELIMITER = "<<<EXTERNAL_UNTRUSTED_CONTENT>>>"
+END_DELIMITER = "<<<END_EXTERNAL_UNTRUSTED_CONTENT>>>"
+
+
+def wrap_untrusted_content(content: Union[str, dict, list]) -> str:
+    """Wrap external content with safety delimiters.
+    
+    This creates a semantic boundary between system instructions
+    and untrusted external data, helping prevent prompt injection.
+    
+    Args:
+        content: Raw content (string, dict, or list)
+        
+    Returns:
+        Delimited string for LLM consumption
+    """
+    if isinstance(content, (dict, list)):
+        text = json.dumps(content, indent=2, ensure_ascii=False)
+    else:
+        text = str(content)
+    
+    return f"{START_DELIMITER}\n{text}\n{END_DELIMITER}"
+
+
+def unwrap_trusted_content(delimited: str) -> str:
+    """Extract content from delimiters (for testing/debugging).
+    
+    Args:
+        delimited: Content wrapped in delimiters
+        
+    Returns:
+        Raw content string
+    """
+    lines = delimited.split('\n')
+    if lines[0] == START_DELIMITER and lines[-1] == END_DELIMITER:
+        return '\n'.join(lines[1:-1])
+    return delimited