feat(notes): add Python SDK for manifest discovery

Create mcp-manifest PyPI package with async support:
- discover(): async manifest resolution from domains/URLs/files
- validate(): schema and semantic validation
- McpManifest.from_file(): parse local manifests
- check_command(): verify command availability on PATH
- Full dataclass models for manifest spec v0.1
- Implements autodiscovery protocol (well-known URL + HTML link tags)
- Zero runtime dependencies, Python 3.10+
- Async/await with asyncio support
- Published as mcp-manifest to PyPI

.gitignore

@@ -0,0 +1,5 @@
+__pycache__/
+*.egg-info/
+dist/
+build/
+.venv/