fix: add real coverage measurement and direct-import tests (#6)

## Summary

The test suite was running scripts via subprocess, which meant
pytest-cov couldn't instrument them — **coverage was silently 0% while
the 90% threshold appeared to pass**. The quality gate this repo ships
to downstream repos was never enforced on itself.

- Make `scripts/` importable (add `__init__.py`, configure
`pythonpath=["."]`)
- Add `--cov=scripts --cov-report=term-missing` to `pyproject.toml`
addopts
- Add 79 direct-import tests across 3 new test files
- Allow `_find_project_root()` to accept an optional start path for
testability

## Coverage: 0% → 92%

| Script | Before | After |
|--------|--------|-------|
| check_lint.py | 0% | 98% |
| check_tests.py | 0% | 95% |
| check_types.py | 0% | 92% |
| check_package.py | 0% | 91% |
| qa.py | 0% | 91% |
| sync.py | 0% | 90% |
| check_spelling.py | 0% | 90% |
| check_security.py | 0% | 88% |
| **Total** | **0%** | **92%** |

## Test plan

- [x] 79 new direct-import tests all pass locally
- [x] Lint and format clean
- [x] Coverage threshold (90%) now actually enforced
- [x] Existing subprocess smoke tests preserved for CI integration
coverage

Author: NWarila

pyproject.toml

@@ -45,8 +45,9 @@ strict = true
 files = ["scripts", "tests"]
 
 [tool.pytest.ini_options]
-addopts = "-ra --import-mode=importlib --cov-fail-under=90"
+addopts = "-ra --import-mode=importlib --cov=scripts --cov-report=term-missing --cov-fail-under=90"
 testpaths = ["tests"]
+pythonpath = ["."]
 
 [tool.codespell]
 skip = ".venv,dist,.git,.mypy_cache,.ruff_cache,.pytest_cache,reference"

scripts/__init__.py

@@ -20,14 +20,14 @@
 SCRIPT_DIR = Path(__file__).resolve().parent
 
 
-def _find_project_root() -> Path:
-    """Walk up from SCRIPT_DIR to find the directory containing pyproject.toml."""
-    d = SCRIPT_DIR
+def _find_project_root(start: Path | None = None) -> Path:
+    """Walk up from *start* (default SCRIPT_DIR) to find pyproject.toml."""
+    d = start or SCRIPT_DIR
     while d != d.parent:
         if (d / "pyproject.toml").exists():
             return d
         d = d.parent
-    print(f"Error: could not find pyproject.toml above {SCRIPT_DIR}", file=sys.stderr)
+    print(f"Error: could not find pyproject.toml above {d}", file=sys.stderr)
     sys.exit(1)