GeezerVison

Summary

Simplifies the CI surface after the lock-generation change:

• One job, one command. validate is now a single make check job — the identical command contributors run locally — on Python 3.11 (floor) and 3.14 (latest). The universal lock already resolves every version between them, so the dropped 3.12/3.13 legs ran the identical suite.
• lock-check folded into the 3.11 leg and reduced to make lock + git diff --exit-code; the printed diff is exactly what to commit.
• Deleted the root requirements.txt and requirements-dev.txt — nothing referenced them (CI, Makefile, and docs all use the locks). Dependencies now have one declaration (pyproject.toml) and two generated locks.

81-line workflow → 49 lines; 2 jobs → 1; 4 matrix legs → 2.

Test plan

• make check + make lock-check pass locally on Python 3.11
• pytest 139 passed
• CI green on 3.11 / 3.14 including the lock-check step

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