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/lib/services/nitro-cleanup.ts

@@ -1,7 +1,7 @@
 import { existsSync, promises as fs } from "node:fs";
 import os from "node:os";
 import { sql } from "drizzle-orm";
-import { db } from "@/lib/db";
+import { queryRows } from "@/lib/db";
 import { getBaseClassname, getSafeClassnameStem } from "@/lib/furni/classname";
 import {
 	DEFAULT_NITRO_SOURCES,
@@ -272,12 +272,12 @@ async function loadValidStems(): Promise<Set<string>> {
 	// fallback), mirroring repair-nitros.ts classname resolution.
 	const validStems = new Set<string>();
 	try {
-		const [result] = (await db.execute(sql`
+		const result = await queryRows<{
+			item_name: string;
+			public_name: string;
+		}>(sql`
 			SELECT item_name, public_name FROM items_base
-		`)) as unknown as [
-			Array<{ item_name: string; public_name: string }>,
-			unknown,
-		];
+		`);
 		for (const row of result) {
 			addStems(validStems, row.item_name);
 			if (