refactor(tests): add shared CLI test helpers

Adds shared test helpers for CLI script loading and scoped core.database stubs, then converts a low-conflict pilot set of CLI tests. Part of #2523.

tests/helpers/db_stubs.py

@@ -0,0 +1,20 @@
+"""Shared database stub helpers for CLI and unit tests."""
+import sys
+import types
+from unittest.mock import MagicMock
+
+
+def make_core_db_stub(monkeypatch, models=()):
+    """Create a core.database stub and inject it via monkeypatch.
+
+    Always sets SessionLocal. Pass model class names via `models` to set
+    each as a MagicMock attribute on the stub.
+
+    Returns the stub module for optional further configuration.
+    """
+    db = types.ModuleType("core.database")
+    db.SessionLocal = MagicMock()
+    for name in models:
+        setattr(db, name, MagicMock())
+    monkeypatch.setitem(sys.modules, "core.database", db)
+    return db