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/upload-import.ts

@@ -1,7 +1,7 @@
 import { existsSync, promises as fs } from "node:fs";
 import path from "node:path";
 import { eq, sql } from "drizzle-orm";
-import { db, ItemsBase } from "@/lib/db";
+import { db, ItemsBase, queryRows } from "@/lib/db";
 import { autoDetectInteraction } from "@/lib/furni/auto-interaction";
 import { logServerError } from "@/lib/server-log";
 import { getFurniAssetWriteTargets } from "@/lib/services/furni-asset-dirs";
@@ -105,9 +105,9 @@ async function allocateItemsBaseId<T>(
 				itemsBaseNextId === null ||
 				Date.now() - itemsBaseIdLastUsed > ITEMS_BASE_ID_REFRESH_MS
 			) {
-				const [idRows] = (await db.execute(sql`
+				const idRows = await queryRows<{ next: number }>(sql`
 					SELECT COALESCE(MAX(id), 0) + 1 AS next FROM items_base
-				`)) as unknown as [Array<{ next: number }>, unknown];
+				`);
 				itemsBaseNextId = Number(idRows[0]?.next ?? 1);
 			}
 		} finally {
@@ -410,9 +410,9 @@ export async function uploadSingleFurni(params: {
 	try {
 		// Skip when the item already has a catalog row — re-uploads must never
 		// create a second row for the same item_ids.
-		const [existingCatalog] = (await db.execute(sql`
+		const existingCatalog = await queryRows<{ id: number }>(sql`
       SELECT id FROM catalog_items WHERE item_ids = ${String(newId)} LIMIT 1
-    `)) as unknown as [Array<{ id: number }>, unknown];
+    `);
 		if (existingCatalog.length > 0) {
 			catalogItemId = existingCatalog[0].id;
 			warnings.push(