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_scatter_chart.md

@@ -0,0 +1,25 @@
+# generate_scatter_chart — 散点图
+
+## 功能概述
+展示两个连续变量之间的关系，可通过颜色/形状区分不同分组，适合相关性分析、聚类探索。
+
+## 输入字段
+### 必填
+- `data`: array<object>，每条记录包含 `x`（number）与 `y`（number），可选 `group`（string）。
+
+### 可选
+- `style.backgroundColor`: string，设置背景色。
+- `style.palette`: string[]，指定系列配色。
+- `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`。
+- `title`: string，默认空字符串。
+- `axisXTitle`: string，默认空字符串。
+- `axisYTitle`: string，默认空字符串。
+
+## 使用建议
+在上传前可对不同量纲进行标准化；若数据量很大可先抽样；使用 `group` 区分不同类别或聚类结果以便阅读。
+
+## 返回结果
+- 返回散点图 URL，并附 `_meta.spec`。