test(genai): add 44 offline tests for commands/docker.py DockerManager

[jsboige]

Summary

Adds comprehensive offline test coverage for commands/docker.py (DockerManager class, 370 lines).

Test classes (44 tests, 0.26s)

Class	Tests	Coverage
TestRunCmd	6	subprocess wrapper: success, failure, timeout, exception, cwd, capture
TestGetContainerStatus	6	Docker inspect mock: unknown, not_found, running, exited, malformed JSON, missing health
TestCheckServiceHealth	9	HTTP health: unknown, 200 OK, 401 auth, connection refused, timeout, bearer auth, basic auth, remote URL, 500 error
TestStartStopService	8	start/stop/restart: unknown, success, failure, missing compose_dir, build flag, stop, restart order
TestGetLogs	3	Docker logs: unknown, known, tail parameter
TestCheckGpu	4	nvidia-smi mock: not found, single GPU, dual GPU, empty output
TestRegisterAndExecute	8	CLI: subparser registration, status/start/stop/logs/test/default dispatch

Design

• Zero external dependencies — no Docker, no nvidia-smi, no network
• All subprocess and HTTP calls mocked via unittest.mock.patch
• Config injected via sys.modules["config"] stub (same pattern as test_genai_audio_models)
• Cross-platform: Windows path assertions use str().replace("\\", "/")

Why

commands/docker.py is the core Docker management module used by genai.py docker status/start/stop/restart/logs/test. Previously had 0 dedicated tests.

Test plan

python -m pytest scripts/notebook_tools/tests/test_genai_docker.py -v
# 44 passed in 0.26s