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/docs/MEMORY_SETTINGS_REVIEW.md

@@ -0,0 +1,63 @@
+# Memory Settings Review
+
+Use this when reviewing the Memory Settings add/edit flow locally with the fewest possible manual steps.
+
+## Quick Review
+
+1. Start DeerFlow locally using any working development setup you already use.
+
+   Examples:
+
+   ```bash
+   make dev
+   ```
+
+   or
+
+   ```bash
+   make docker-start
+   ```
+
+   If you already have DeerFlow running locally, you can reuse that existing setup.
+
+2. Load the sample memory fixture.
+
+   ```bash
+   python scripts/load_memory_sample.py
+   ```
+
+3. Open `Settings > Memory`.
+
+   Default local URLs:
+   - App: `http://localhost:2026`
+   - Local frontend-only fallback: `http://localhost:3000`
+
+## Minimal Manual Test
+
+1. Click `Add fact`.
+2. Create a new fact with:
+   - Content: `Reviewer-added memory fact`
+   - Category: `testing`
+   - Confidence: `0.88`
+3. Confirm the new fact appears immediately and shows `Manual` as the source.
+4. Edit the sample fact `This sample fact is intended for edit testing.` and change it to:
+   - Content: `This sample fact was edited during manual review.`
+   - Category: `testing`
+   - Confidence: `0.91`
+5. Confirm the edited fact updates immediately.
+6. Refresh the page and confirm both the newly added fact and the edited fact still persist.
+
+## Optional Sanity Checks
+
+- Search `Reviewer-added` and confirm the new fact is matched.
+- Search `workflow` and confirm category text is searchable.
+- Switch between `All`, `Facts`, and `Summaries`.
+- Delete the disposable sample fact `Delete fact testing can target this disposable sample entry.` and confirm the list updates immediately.
+- Clear all memory and confirm the page enters the empty state.
+
+## Fixture Files
+
+- Sample fixture: `backend/docs/memory-settings-sample.json`
+- Default local runtime target: `backend/.deer-flow/memory.json`
+
+The loader script creates a timestamped backup automatically before overwriting an existing runtime memory file.