fix(python): prepare sdk publishing

[samzong]

Summary

• Publish the Python SDK as the kitup-sdk PyPI distribution while keeping the kitup import package.
• Fix Python workflow stdin handling and Python 3.10 compatibility.
• Add release guards for PyPI publishing, canonical Go module checks, and Python version support.

Scope Check

• Stays within the v0.1 bundled-skill installer boundary.
• Does not add marketplace, registry, remote install, script execution, GUI, MCP server, or agent runtime behavior.
• No golden case update required; no cross-language installer behavior changed.
• No spec/hosts.json changes; host constants unchanged.

Verification

• make check
• uv run --directory python --python 3.10 pytest tests -q
• Python SDK tests passed on 3.10, 3.11, 3.12, 3.13, and 3.14 locally.