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/app/api/tickets/route.ts

@@ -5,7 +5,6 @@
 // DB errors return an apiError envelope, never a 500.
 
 import { desc, eq } from "drizzle-orm";
-import type { ResultSetHeader } from "mysql2";
 import { apiError, apiJson, positiveBigInt } from "@/lib/api";
 import { bearerUserId } from "@/lib/api-auth";
 import { db, WebsiteHelpCenterTickets } from "@/lib/db";
@@ -79,7 +78,7 @@ export async function POST(req: Request) {
 
 	try {
 		const now = new Date();
-		const [result] = (await db.insert(WebsiteHelpCenterTickets).values({
+		const [result] = await db.insert(WebsiteHelpCenterTickets).values({
 			userId: uid,
 			categoryId,
 			title,
@@ -87,7 +86,7 @@ export async function POST(req: Request) {
 			open: true,
 			createdAt: now,
 			updatedAt: now,
-		})) as unknown as [ResultSetHeader];
+		});
 
 		return apiJson(
 			{