feat: Engine+Schema fuer Szenario-Ende und szenario-eigene Einmalzahlungen

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/tests/test_models.py

@@ -22,3 +22,15 @@ def test_account_transaction_roundtrip(db):
     db.add(tx)
     db.commit()
     assert db.query(Transaction).one().amount == Decimal("-50.00")
+
+
+def test_scenario_planned_item_roundtrip(db):
+    from app.models.tables import Scenario, ScenarioPlannedItem
+    sc = Scenario(name="SPI-Test", description="")
+    db.add(sc)
+    db.flush()
+    db.add(ScenarioPlannedItem(scenario_id=sc.id, name="Einmalzahlung",
+                               amount=Decimal("5000.00"), due=date(2026, 7, 30)))
+    db.commit()
+    item = db.query(ScenarioPlannedItem).one()
+    assert item.amount == Decimal("5000.00") and item.scenario_id == sc.id