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/app/gateway/routers/channels.py

@@ -0,0 +1,52 @@
+"""Gateway router for IM channel management."""
+
+from __future__ import annotations
+
+import logging
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/api/channels", tags=["channels"])
+
+
+class ChannelStatusResponse(BaseModel):
+    service_running: bool
+    channels: dict[str, dict]
+
+
+class ChannelRestartResponse(BaseModel):
+    success: bool
+    message: str
+
+
+@router.get("/", response_model=ChannelStatusResponse)
+async def get_channels_status() -> ChannelStatusResponse:
+    """Get the status of all IM channels."""
+    from app.channels.service import get_channel_service
+
+    service = get_channel_service()
+    if service is None:
+        return ChannelStatusResponse(service_running=False, channels={})
+    status = service.get_status()
+    return ChannelStatusResponse(**status)
+
+
+@router.post("/{name}/restart", response_model=ChannelRestartResponse)
+async def restart_channel(name: str) -> ChannelRestartResponse:
+    """Restart a specific IM channel."""
+    from app.channels.service import get_channel_service
+
+    service = get_channel_service()
+    if service is None:
+        raise HTTPException(status_code=503, detail="Channel service is not running")
+
+    success = await service.restart_channel(name)
+    if success:
+        logger.info("Channel %s restarted successfully", name)
+        return ChannelRestartResponse(success=True, message=f"Channel {name} restarted successfully")
+    else:
+        logger.warning("Failed to restart channel %s", name)
+        return ChannelRestartResponse(success=False, message=f"Failed to restart channel {name}")