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/navigation/page.tsx

@@ -2,7 +2,13 @@ import { asc, inArray, sql } from "drizzle-orm";
 import { redirect } from "next/navigation";
 import { getTranslations } from "next-intl/server";
 import { StatusCard } from "@/components/admin/dashboard";
-import { db, NavigatorFlatcats, NavigatorPubliccats, Rooms } from "@/lib/db";
+import {
+	db,
+	NavigatorFlatcats,
+	NavigatorPubliccats,
+	queryRows,
+	Rooms,
+} from "@/lib/db";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 
 // navigator_flatcats — emulator-owned flat (private-room) categories shown in the
@@ -65,12 +71,11 @@ export default async function AdminNavigation() {
 
 	let publics: PublicRow[] = [];
 	try {
-		const [rows] = (await db.execute(sql`
+		publics = await queryRows<PublicRow>(sql`
       SELECT public_cat_id, room_id, visible
       FROM navigator_publics
       ORDER BY public_cat_id ASC, room_id ASC
-    `)) as unknown as [PublicRow[], unknown];
-		publics = rows ?? [];
+    `);
 	} catch {
 		publics = [];
 	}