QA: add structural and model tests for story 1.1 scaffold

Replaces placeholder stubs in test_models.py, test_gpio_ctrl.py, and
provisioning/test_provision_loop.py with real assertions. Adds new
test_scaffold.py covering AC3 file-presence, importlib.resources
airports.csv load, constants completeness, and main.py provisioning
import guard. Extends ruff per-file-ignores so tests/provisioning/*.py
may import from planemapper.provisioning. All 22 tests pass; ruff
check and format --check both clean.

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

tests/provisioning/test_provision_loop.py

@@ -1,2 +1,12 @@
-def test_placeholder() -> None:
-    pass
+from planemapper.provisioning import ProvisioningError
+
+
+def test_provisioning_error_is_exception() -> None:
+    assert issubclass(ProvisioningError, Exception)
+
+
+def test_provisioning_error_can_be_raised_and_caught() -> None:
+    try:
+        raise ProvisioningError("test error")
+    except ProvisioningError as e:
+        assert str(e) == "test error"