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/admin/subscriptions/page.tsx

@@ -4,7 +4,7 @@ import { getTranslations } from "next-intl/server";
 import { AdminSimplePager } from "@/components/admin/admin-simple-pager";
 import { StatusCard } from "@/components/admin/dashboard";
 import { calcPagination, parseListParams } from "@/lib/admin-helpers";
-import { db } from "@/lib/db";
+import { queryRows } from "@/lib/db";
 import { formatDate } from "@/lib/format-date";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 
@@ -24,8 +24,7 @@ type SubSqlRow = {
 };
 
 async function rawRows<T>(query: ReturnType<typeof sql>): Promise<T[]> {
-	const [rows] = (await db.execute(query)) as unknown as [T[], unknown];
-	return rows ?? [];
+	return queryRows<T>(query);
 }
 
 export default async function AdminSubscriptions({