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/upload-import.test.ts

@@ -33,7 +33,8 @@ vi.mock("drizzle-orm", () => ({
 	}),
 }));
 
-vi.mock("@/lib/db", () => ({
+vi.mock("@/lib/db", async () => ({
+	...(await import("@/test/db-helpers")).createDbHelpers(dbExecuteMock),
 	ItemsBase: { id: "id", itemName: "item_name" },
 	db: {
 		execute: dbExecuteMock,