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/admin/installation.ts

@@ -9,7 +9,7 @@ import {
 	workerState,
 } from "@/lib/admin/installation-state";
 import { fetchOpsHealth } from "@/lib/admin/ops-health";
-import { db } from "@/lib/db";
+import { queryRows } from "@/lib/db";
 import { redis } from "@/lib/redis";
 import { siteSettings } from "@/lib/services/site-settings";
 
@@ -36,13 +36,10 @@ export async function inspectInstallation() {
 						.map((name) => name.slice(0, -4)),
 				)
 				.catch(() => []),
-			db
-				.execute(sql`SELECT migration FROM cms_migrations`)
-				.then(([rows]) =>
-					(rows as unknown as { migration: string }[]).map(
-						(row) => row.migration,
-					),
-				)
+			queryRows<{ migration: string }>(
+				sql`SELECT migration FROM cms_migrations`,
+			)
+				.then((rows) => rows.map((row) => row.migration))
 				.catch(() => null),
 			redis
 				? redis.get("cms:jobs-worker:heartbeat").catch(() => null)