fix: make lint usable for critical checks

[wayyoungboy]

Summary

Closes #275.

This PR makes the default make lint target usable as a high-signal regression gate instead of reporting the full historical style backlog.

Changes:

• adds an explicit Python >= 3.11 guard through the configurable PYTHON make variable
• changes default make lint to check critical flake8 errors only: duplicate dict keys, undefined names, and syntax errors
• moves the full flake8 report to make lint-full
• keeps pylint available as optional make lint-pylint, so the default target no longer depends on a tool that is not installed by the current dev extras
• fixes the currently reported critical lint failures

Validation

• PYTHON=<python3.11> make lint
• PYTHON=python3 make lint verifies the version guard reports a clear Python >= 3.11 requirement when the default interpreter is too old
• git diff --check

[lightzt99]

LGTM