test: rewrite test_database_audit using mem_db fixture, no disk writes required

tests/test_database_audit.py

@@ -0,0 +1,26 @@
+"""Tests for MotionDatabase.append_audit_event — no filesystem side effects on audit path."""
+
+
+def test_append_audit_event_returns_true(mem_db):
+    """append_audit_event should succeed (DB or ledger fallback) and return True."""
+    ok = mem_db.append_audit_event(
+        actor_id=None,
+        action="test_action",
+        target_type="unit",
+        target_id="u1",
+        metadata={"k": 1},
+    )
+    assert ok is True
+
+
+def test_append_audit_event_does_not_raise_on_bad_db(mem_db):
+    """Even if DB insert fails, the method falls back and doesn't raise."""
+    ok = mem_db.append_audit_event(
+        actor_id=None,
+        action="another_action",
+        target_type="motion",
+        target_id=None,
+        metadata={},
+    )
+    # Returns True or False, but must not raise
+    assert isinstance(ok, bool)