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/features/history/history.test.ts

@@ -2,7 +2,11 @@ import type { SQL } from "drizzle-orm";
 import { MySqlDialect } from "drizzle-orm/mysql-core";
 import { describe, expect, it, vi } from "vitest";
 
-vi.mock("@/lib/db", async () => ({ ...(await import("@/db/schema")), db: {} }));
+vi.mock("@/lib/db", async () => ({
+	...(await import("@/db/schema")),
+	rowsFrom: (await import("@/test/db-helpers")).rowsFrom,
+	db: {},
+}));
 
 import { historyChanges, sameSnapshot } from "./model";
 import {