chore: require Python 3.11

[d33bs]

Summary

• Raise the minimum Python version from 3.10 to 3.11 while keeping the existing 3.12 upper bound.
• Update the lockfile, CI matrix, lint target, and documentation.

Verification

• Python 3.11.13: uv sync --frozen --python 3.11 --group dev
• uv run --frozen --python 3.11 ruff check . — passed
• uv run --frozen --python 3.11 pytest — 51 passed, 4 integration tests deselected
• uv build — passed; wheel metadata reports Requires-Python: <3.12,>=3.11.

Integration tests requiring external model downloads were not run locally.