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/actions/applications.test.ts

@@ -3,6 +3,7 @@ import { redirect } from "next/navigation";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { auth } from "@/lib/auth";
 import { clientIp, rateLimit } from "@/lib/rate-limit";
+import { fakeForm } from "@/test/fake-form";
 import { applyStaff, applyTeam } from "./applications";
 
 const { selectLimit, insertValues } = vi.hoisted(() => {
@@ -33,10 +34,6 @@ vi.mock("@/lib/rate-limit", () => ({ clientIp: vi.fn(), rateLimit: vi.fn() }));
 vi.mock("next/cache", () => ({ revalidatePath: vi.fn() }));
 vi.mock("next/navigation", () => ({ redirect: vi.fn() }));
 
-const fakeForm = (data) => ({
-	get: (key) => data[key] ?? null,
-});
-
 beforeEach(() => {
 	vi.clearAllMocks();
 	vi.mocked(auth).mockResolvedValue({ user: { id: "42" } });