fix(knowledge): keep PATCH category moves inside knowledge/

[dani1005]

Summary

PATCH /knowledge/documents/{doc_id} sanitized a new category_id with a private copy of the dirname rule (_safe_category) that lacked the . / .. fallback of the shared sanitize_dirname. With category_id: ".." the document directory was moved from knowledge/<category>/ up into the project directory, where the md-scan fallback no longer finds it (and an index rebuild from markdown would drop it). Reported privately; impact is limited to data the caller can already modify through the API, so it is handled as hardening per the threat model in SECURITY.md.

• Fix (service/knowledge.py): drop _safe_category; the move target is knowledge_dir(app, project) / sanitize_dirname(category, "Others") / <doc dir>, so . / .. fall back to Others exactly as on create. The resolved target is asserted to stay inside knowledge/ before any directory is created or moved (PathTraversalError otherwise). A document an earlier move left outside is moved back on its next category change.
• SECURITY.md: supported versions 1.2.x → 1.4.x; add a "what counts as a vulnerability" line under Scope.
• CHANGELOG.md: [Unreleased] → Fixed entry.

An audit of the other places where external input becomes a path segment (app/project/sender ids, upload filename, create-time category/title/topic, skill/reference/script names, profile writes) found no other instance; they all go through PathSafeId, sanitize_dirname, or MarkdownWriter._ensure_within_root.

Area

• Architecture method
• Benchmark
• Use case
• Documentation
• Developer experience
• CI, build, or release

Verification

make lint                     # ruff, import-linter (4 contracts kept), asset/size/datetime/openapi/docs gates
uv run pytest tests/unit      # 2618 passed, 4 skipped
uv run pytest tests/integration  # 186 passed, 5 skipped, 7 deselected
make package                  # wheel/sdist smoke OK

New tests in tests/unit/test_service/test_knowledge_crud.py (real filesystem): category Research Notes / .. / . stay in knowledge/; an escaped doc is repaired; a category dir symlinked outside knowledge/ raises PathTraversalError. The .., . and symlink cases fail against the previous code.

Checklist

• I kept the change scoped to the relevant area.
• I am opening this from a separate branch, not pushing directly to main.
• I updated docs, examples, or setup notes when behavior changed.
• I added or updated tests when the change affects behavior.
• I did not commit secrets, .env files, dependency folders, or generated output.
• Active relative links in Markdown files resolve.

Notes for Reviewers

• The stored category_id metadata keeps the raw value (as on create); only the directory segment is sanitized.
• _require_knowledge_capabilities is a feature-tier gate (embed + rerank), not authorization, so PATCH intentionally stays without it.
• The SECURITY.md scope wording is a policy statement — please review it as such.

By submitting this pull request, I agree that my contribution is licensed under
the Apache License 2.0.

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