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/badges/leaderboard/route.ts

@@ -3,7 +3,7 @@ import { connection } from "next/server";
 import { apiJson } from "@/lib/api";
 import { bearerUserId } from "@/lib/api-auth";
 import { auth } from "@/lib/auth";
-import { db, User, UsersSettings } from "@/lib/db";
+import { db, queryRows, User, UsersSettings } from "@/lib/db";
 import { logger } from "@/lib/logger";
 import { apiCacheKey, cacheSafe, redisCache } from "@/lib/redis-cache";
 
@@ -68,8 +68,7 @@ function rankEntries(
 }
 
 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);
 }
 
 async function loadTotalBadgesBoard(): Promise<BoardCore> {