fix(showcase): resync scripts lockfile after aimock 1.26.1 bump

PR #4956 bumped @copilotkit/aimock in showcase/scripts/package.json
from "latest" to "1.26.1" but did not regenerate package-lock.json
(still pinned to 1.16.4). This broke the Showcase Docker builds for
showcase-harness and shell-dashboard, since both run `npm ci` inside
showcase/scripts/ and `npm ci` fails on out-of-sync lockfiles.