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-integrity-audit.test.ts

@@ -8,7 +8,10 @@ const mocks = vi.hoisted(() => ({
 	repair: vi.fn(),
 }));
 vi.mock("node:fs/promises", () => ({ readdir: mocks.readdir }));
-vi.mock("@/lib/db", () => ({ db: { execute: mocks.execute } }));
+vi.mock("@/lib/db", async () => ({
+	...(await import("@/test/db-helpers")).createDbHelpers(mocks.execute),
+	db: { execute: mocks.execute },
+}));
 vi.mock("@/lib/services/clone-import", () => ({}));
 vi.mock("@/lib/services/clone-sources", () => ({}));
 vi.mock("@/lib/services/furni-asset-dirs", () => ({