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/pyproject.toml

@@ -0,0 +1,29 @@
+[project]
+name = "deer-flow"
+version = "0.1.0"
+description = "LangGraph-based AI agent system with sandbox execution capabilities"
+readme = "README.md"
+requires-python = ">=3.12"
+dependencies = [
+    "deerflow-harness",
+    "fastapi>=0.115.0",
+    "httpx>=0.28.0",
+    "python-multipart>=0.0.20",
+    "sse-starlette>=2.1.0",
+    "uvicorn[standard]>=0.34.0",
+    "lark-oapi>=1.4.0",
+    "slack-sdk>=3.33.0",
+    "python-telegram-bot>=21.0",
+    "langgraph-sdk>=0.1.51",
+    "markdown-to-mrkdwn>=0.3.1",
+    "wecom-aibot-python-sdk>=0.1.6",
+]
+
+[dependency-groups]
+dev = ["pytest>=8.0.0", "ruff>=0.14.11"]
+
+[tool.uv.workspace]
+members = ["packages/harness"]
+
+[tool.uv.sources]
+deerflow-harness = { workspace = true }