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/podcast-generation/templates/tech-explainer.md

@@ -0,0 +1,63 @@
+# Tech Explainer Podcast Template
+
+Use this template when converting technical documentation, API guides, or developer tutorials into podcasts.
+
+## Input Preparation
+
+When the user wants to convert technical content to a podcast, help them structure the input:
+
+1. **Simplify Code Examples**: Replace code snippets with plain language descriptions
+   - Instead of showing actual code, describe what the code does
+   - Focus on concepts rather than syntax
+
+2. **Remove Complex Notation**:
+   - Mathematical formulas should be explained in words
+   - API endpoints described by function rather than URL paths
+   - Configuration examples summarized as settings descriptions
+
+3. **Add Context**:
+   - Explain why the technology matters
+   - Include real-world use cases
+   - Add analogies for complex concepts
+
+## Example Transformation
+
+### Original Technical Content:
+```markdown
+# Using the API
+
+POST /api/v1/users
+{
+  "name": "John",
+  "email": "john@example.com"
+}
+
+Response: 201 Created
+```
+
+### Podcast-Ready Content:
+```markdown
+# Creating Users with the API
+
+The user creation feature allows applications to register new users in the system.
+When you want to add a new user, you send their name and email address to the server.
+If everything goes well, the server confirms the user was created successfully.
+This is commonly used in signup flows, admin dashboards, or when importing users from other systems.
+```
+
+## Generation Command
+
+```bash
+python /mnt/skills/public/podcast-generation/scripts/generate.py \
+  --script-file /mnt/user-data/workspace/tech-explainer-script.json \
+  --output-file /mnt/user-data/outputs/tech-explainer-podcast.mp3 \
+  --transcript-file /mnt/user-data/outputs/tech-explainer-transcript.md
+```
+
+## Tips for Technical Podcasts
+
+- Keep episodes focused on one main concept
+- Use analogies to explain abstract concepts
+- Include practical "why this matters" context
+- Avoid jargon without explanation
+- Make the dialogue accessible to beginners