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

docker-compose.yml

@@ -5,6 +5,8 @@ services:
       - "${PORT:-8010}:8000"
     env_file:
       - .env
+    volumes:
+      - /tmp:/tmp
     restart: unless-stopped
     healthcheck:
       test: ["CMD", "python", "-c", "import httpx; httpx.get('http://localhost:8000/health').raise_for_status()"]