Add addon-load smoke test pinning register/unregister cycle

Surfaces any regression in:

* the modules dict in bim/__init__.py (added a folder, forgot the entry)
* PointerProperty wiring on bpy.types.{Scene,Object,...}
* registry-driven GizmoPreferences<Name> auto-registration in
  tool.Parametric.iter_gizmo_preference_classes
* bpy.app.handlers append/remove balance
* every register()/unregister() across the 45+ feature modules

as a single PASSED/FAILED test instead of the silent "addon failed to
enable" users encounter in a fresh Blender. Paired with the existing
test_parametric_registry.py contract tests, this catches both the
registry-shape regressions (operators/PropertyGroups/predicates) and
the registration-mechanics regressions (PointerProperty types not
registered before their owners).

Generated with the assistance of an AI coding tool.

src/bonsai/test/bim/test_addon_lifecycle.py

@@ -0,0 +1,60 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2026
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file was generated with the assistance of an AI coding tool.
+
+"""Addon-load smoke for ``bonsai``.
+
+Pins the registration/unregistration cycle as a runnable contract. The cycle
+exercises every ``register()`` site across ``bim/__init__.py``'s modules dict,
+every ``PointerProperty`` attachment, every gizmo-prefs auto-registration, and
+every ``bpy.app.handlers`` install. A regression in any of those surfaces here
+as an exception with a traceback that points at the failing site, instead of
+the silent ``addon failed to enable`` users see in a fresh Blender."""
+
+import types
+
+import bpy
+import pytest
+
+pytestmark = pytest.mark.model
+
+
+@pytest.fixture(autouse=True)
+def _require_real_bpy():
+    if not isinstance(bpy, types.ModuleType) or hasattr(bpy, "_mock_name"):
+        pytest.skip("requires real Blender (bpy is mocked or absent)")
+
+
+def test_addon_unregister_then_register_does_not_raise():
+    """Running the suite has already enabled the addon. Cycle through one
+    unregister + register to exercise both halves, then leave the addon
+    enabled so downstream tests in the same Blender session keep working."""
+    import bonsai
+
+    bonsai.unregister()
+    try:
+        bonsai.register()
+    except Exception:
+        # Re-raise after attempting to leave the session in a usable state for
+        # any tests that run after this one.
+        try:
+            bonsai.register()
+        except Exception:
+            pass
+        raise