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/actions/admin-ads.ts

@@ -1,7 +1,6 @@
 "use server";
 
 import { eq } from "drizzle-orm";
-import type { ResultSetHeader } from "mysql2";
 import { revalidatePath } from "next/cache";
 import { redirect } from "next/navigation";
 import { z } from "zod";
@@ -26,11 +25,11 @@ export async function createAd(formData: FormData): Promise<void> {
 
 	const now = new Date();
 	try {
-		const [result] = (await db.insert(WebsiteAds).values({
+		const [result] = await db.insert(WebsiteAds).values({
 			image,
 			createdAt: now,
 			updatedAt: now,
-		})) as unknown as [ResultSetHeader];
+		});
 		await logStaffActivity({
 			staffId: staff.id,
 			action: "ad_create",
@@ -95,9 +94,7 @@ export const deleteAd = adminAction(
 	async (ctx) => {
 		const id = ctx.data.id;
 		try {
-			const [result] = (await db
-				.delete(WebsiteAds)
-				.where(eq(WebsiteAds.id, id))) as unknown as [ResultSetHeader];
+			const [result] = await db.delete(WebsiteAds).where(eq(WebsiteAds.id, id));
 			if (!result.affectedRows) {
 				throw new ActionError("Advertisement not found");
 			}