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/users/_lib/load-user-overview.ts

@@ -1,5 +1,5 @@
 import { type SQL, sql } from "drizzle-orm";
-import { db } from "@/lib/db";
+import { queryRows } from "@/lib/db";
 import { canAccess, PERMS, type PermissionSet } from "@/lib/permissions";
 
 export type OverviewRow = {
@@ -27,8 +27,7 @@ export async function loadUserOverview(
 	rank: number,
 ): Promise<OverviewSection[]> {
 	const read = async (query: SQL): Promise<OverviewRow[]> => {
-		const [rows] = await db.execute(query);
-		return rows as unknown as OverviewRow[];
+		return queryRows<OverviewRow>(query);
 	};
 	const sources: {
 		key: string;