Add minimal pytest smoke tests and GitHub Actions CI

[rosspeili]

Problem

There is no tests/ tree; regressions in import order, gating, or env handling are caught only manually.

Goal

• Add a few offline tests: import selected modules with env patched/mocked, or subprocess smoke python -c "import OPSIIE_0_3_80_XP" with minimal env (design around current Web3 coupling or land after lazy-Web3 issue).
• GitHub Action: run pytest on PR/push to default branch; optional ruff/black --check if the team agrees.

Acceptance criteria

• pytest passes in CI without real API keys or camera.
• CONTRIBUTING or README points to how to run tests locally.