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/config/skills_config.py

@@ -0,0 +1,54 @@
+from pathlib import Path
+
+from pydantic import BaseModel, Field
+
+
+def _default_repo_root() -> Path:
+    """Resolve the repo root without relying on the current working directory."""
+    return Path(__file__).resolve().parents[5]
+
+
+class SkillsConfig(BaseModel):
+    """Configuration for skills system"""
+
+    path: str | None = Field(
+        default=None,
+        description="Path to skills directory. If not specified, defaults to ../skills relative to backend directory",
+    )
+    container_path: str = Field(
+        default="/mnt/skills",
+        description="Path where skills are mounted in the sandbox container",
+    )
+
+    def get_skills_path(self) -> Path:
+        """
+        Get the resolved skills directory path.
+
+        Returns:
+            Path to the skills directory
+        """
+        if self.path:
+            # Use configured path (can be absolute or relative)
+            path = Path(self.path)
+            if not path.is_absolute():
+                # If relative, resolve from the repo root for deterministic behavior.
+                path = _default_repo_root() / path
+            return path.resolve()
+        else:
+            # Default: ../skills relative to backend directory
+            from deerflow.skills.loader import get_skills_root_path
+
+            return get_skills_root_path()
+
+    def get_skill_container_path(self, skill_name: str, category: str = "public") -> str:
+        """
+        Get the full container path for a specific skill.
+
+        Args:
+            skill_name: Name of the skill (directory name)
+            category: Category of the skill (public or custom)
+
+        Returns:
+            Full path to the skill in the container
+        """
+        return f"{self.container_path}/{category}/{skill_name}"