Define supported Python versions and test matrix for v1.0

[devgamesan]

Context

pyproject.toml declares requires-python = ">=3.12", while CI currently tests only Python 3.12. Local testing has also run on Python 3.13. Before v1.0, the supported version policy should be explicit and enforced.

Tasks

• Decide whether v1.0 supports Python 3.12 only or Python 3.12 and 3.13.
• If 3.13 is supported, add a CI matrix for 3.12 and 3.13.
• If only 3.12 is supported, tighten documentation and/or package metadata accordingly.
• Verify uv.lock and dependency constraints remain compatible with the chosen policy.

Acceptance Criteria

• CI covers every Python version claimed as supported.
• pyproject.toml, README, and release notes do not imply unsupported Python versions.
• The v1.0 release checklist includes the selected Python version policy.