feat: add binary file attachment and import tools for Outline LTM system (#1)

Implement 3 new MCP tools:
- attach_file_to_document(document_id, file_path)
- upload_image_to_document(image_path, document_id, alt_text)
- import_file_to_outline(file_path, collection_id, parent_document_id)

Security:
- Restrict file access to /tmp via _validate_file_path with realpath
- 50MB max file size enforced client-side
- Symlink traversal blocked

Technical:
- Extract shared _upload_attachment() helper
- Stream files to presigned URLs instead of loading into memory
- Add combined lifespan to close OutlineClient on shutdown
- Update CI workflow with modern action versions and PR triggers

Tests:
- Add 28 tests covering path validation, size limits, upload flow,
  error handling, symlink traversal, and multipart imports

.gitignore

@@ -0,0 +1,5 @@
+venv/
+__pycache__/
+*.egg-info/
+.pytest_cache/
+.ruff_cache/