Fix schema

postgres/schema/0004_user_budgets.sql

@@ -0,0 +1,8 @@
+-- +goose Up
+CREATE TABLE user_budgets (
+    user_id uuid NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    budget_id uuid NOT NULL REFERENCES budgets (id) ON DELETE CASCADE
+);
+
+-- +goose Down
+DROP TABLE user_budgets;