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/catalog-parent-repair.test.ts

@@ -7,7 +7,8 @@ const mocks = vi.hoisted(() => ({
 	insert: vi.fn(),
 	values: vi.fn(),
 }));
-vi.mock("@/lib/db", () => ({
+vi.mock("@/lib/db", async () => ({
+	...(await import("@/test/db-helpers")).createDbHelpers(mocks.execute),
 	AdminAuditLog: "audit",
 	db: { execute: mocks.execute, transaction: mocks.transaction },
 }));