feat: add budget folder schema and migration

src/ui/components/ExpectedBand.test.ts

@@ -65,6 +65,7 @@ function cost(overrides: Partial<RecurringCost> = {}): RecurringCost {
     id: "r1",
     name: "Rent",
     order: 0,
+    folderId: null,
     archived: false,
     amount: { amount: 8000, currency: "DKK" },
     startDate: "2026-01",