refactor(db): typed query helpers, shared test FormData helper

Replace raw db.execute tuple casts with queryRows/rowsFrom/execResult/
affectedRows helpers from lib/db, drop redundant mysql2 casts on typed
query builders, and centralize per-test fakeForm into test/fake-form.
Update db mocks in tests so helpers resolve against mocked execute.

src/lib/services/furni-maintenance.test.ts

@@ -12,8 +12,8 @@ const state = vi.hoisted(() => ({
 	queries: [] as { sql: string; params: unknown[] }[],
 	writes: 0,
 }));
-vi.mock("@/lib/db", () => ({
-	db: {
+vi.mock("@/lib/db", async () => {
+	const db = {
 		execute: async (query: SQL) => {
 			const compiled = new MySqlDialect().sqlToQuery(query);
 			if (compiled.sql.includes("FROM catalog_items ci"))
@@ -50,8 +50,12 @@ vi.mock("@/lib/db", () => ({
 				},
 			});
 		},
-	},
-}));
+	};
+	return {
+		db,
+		...(await import("@/test/db-helpers")).createDbHelpers(db.execute),
+	};
+});
 
 import { fixEmulatorIssues, listEmulatorIssues } from "./furni-maintenance";