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/skills/public/chart-visualization/references/generate_flow_diagram.md

@@ -0,0 +1,22 @@
+# generate_flow_diagram — 流程图
+
+## 功能概述
+以节点和连线展示业务流程、审批链或算法步骤，支持开始/判断/操作等多种节点类型。
+
+## 输入字段
+### 必填
+- `data`: object，必填，包含节点与连线定义。
+- `data.nodes`: array<object>，至少 1 条，节点需提供唯一 `name`。
+- `data.edges`: array<object>，至少 1 条，包含 `source` 与 `target`（string），可选 `name` 作为连线文本。
+
+### 可选
+- `style.texture`: string，默认 `default`，可选 `default`/`rough`。
+- `theme`: string，默认 `default`，可选 `default`/`academy`/`dark`。
+- `width`: number，默认 `600`。
+- `height`: number，默认 `400`。
+
+## 使用建议
+先罗列节点 `name` 并保持唯一，再建立连线；若需要描述条件，可在 `edges.name` 中填写；流程应保持单向或明确分支避免交叉。
+
+## 返回结果
+- 返回流程图 URL，并携带 `_meta.spec` 中的节点与边数据，方便下次调整。