Initial Migration: Move Python SDK to standalone repo and recreate MkDocs pipeline

[huangjeff5]

This PR serves as the official migration of the Python SDK into its new standalone repository (genkit-python).

Key Changes:

1. Repository Migration: Moved all Python SDK packages, tools, and configurations out of the monolithic genkit repository and into this dedicated standalone repo. Relative paths in scripts (like justfile and generate_schema_typing) have been updated to reflect the flattened directory structure.
2. Recreated MkDocs Pipeline: Reinstated the API documentation pipeline by adding mkdocs.yml and mkdocstrings.
3. Fixed Plugin V2 Alias Resolution: Added missing __init__.py files to private directories (like _ai and _core) so Griffe successfully parses them as modules and correctly resolves the aliases in the API reference.
4. Docs Deployment Pipeline: Added a manual GitHub Actions workflow (deploy_docs.yml) that can be triggered via workflow_dispatch to automatically build the MkDocs site, clone hosting-templates, copy the HTML files, and deploy to Firebase.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.