ci: add notify-failure, pytest with coverage, and 49 unit tests

- lint.yml: add notify-failure Matrix alert job
- test.yml: new workflow running pytest with pytest-cov for coverage
- .coveragerc: omit tests and site-packages from coverage
- .gitignore: ignore __pycache__ and .pyc files
- tests/test_hwmon.py: 49 unit tests covering SystemHealthMonitor
  (temperature parsing, service monitoring, disk usage, metric collection,
  dry run behaviour); uses unittest.mock to isolate from env/filesystem

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.coveragerc

@@ -0,0 +1,7 @@
+[run]
+omit =
+    tests/*
+    */site-packages/*
+
+[report]
+show_missing = True