build: uplift Python kata baseline

[megabyde]

Summary

• require Python 3.11 and use the locked pytest 9.1.1 and Ruff 0.16.1 toolchain
• standardize Make targets, three-platform CI, ownership, and weekly dependency updates
• document reproducible setup while preserving the tennis scoring rules, starter implementation, and tests

Verification

• default make and make help
• UV_CACHE_DIR=/tmp/tennis-python-kata-uv-cache uv lock --check
• UV_CACHE_DIR=/tmp/tennis-python-kata-uv-cache make format-check
• UV_CACHE_DIR=/tmp/tennis-python-kata-uv-cache make test
• parsed workflow and Dependabot YAML
• make clean cache-removal and preservation checks
• git diff --check origin/main...HEAD

Required checks

• lint
• test (ubuntu-latest)
• test (macos-latest)
• test (windows-latest)