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/news-scheduler.test.ts

@@ -22,7 +22,7 @@ const state = vi.hoisted(() => ({
 }));
 vi.mock("@/lib/logger", () => ({ logger: { error: vi.fn() } }));
 vi.mock("./news-cache", () => ({ invalidateNewsCache: state.refresh }));
-vi.mock("@/lib/db", () => {
+vi.mock("@/lib/db", async () => {
 	const dialect = new MySqlDialect();
 	const timestamp = (value: unknown) =>
 		value instanceof Date
@@ -68,6 +68,7 @@ vi.mock("@/lib/db", () => {
 		},
 	};
 	return {
+		rowsFrom: (await import("@/test/db-helpers")).rowsFrom,
 		db: {
 			transaction: async (work: (tx: unknown) => Promise<unknown>) => {
 				state.transactionCalls++;