chore(showcase): bump @copilotkit/aimock to 1.16.4

Picks up the router fix from CopilotKit/aimock#148 — `toolCallId` matchers
now only fire when the tool message is the *last* message in the request,
preventing stale tool_call_ids from history shadowing `userMessage`
matchers on new user turns.

Surfaced as: in beautiful-chat, clicking a second suggestion replayed the
prior chart's "Pie chart rendered above…" content fixture instead of
producing a new tool call. Once Railway rebuilds `ghcr.io/copilotkit/aimock:latest`
and restarts the service, demos will pick up the fix automatically.

- Refresh `pnpm-lock.yaml` resolutions (workspace `@copilotkit/runtime` devDep)
- Refresh `showcase/scripts/package-lock.json` to 1.16.4
- Bump the floor in `test_e2e-showcase-on-demand.yml` from `^1.14.3` → `^1.16.4`
  so the `/test-aimock` PR-comment workflow always installs a build that
  contains the fix

Author: AlemTuzlak

.github/workflows/test_e2e-showcase-on-demand.yml

@@ -264,9 +264,9 @@ jobs:
           # An unrestricted `@latest` means a bad aimock publish silently
           # poisons CI for everyone; pinning makes the upgrade explicit and
           # keeps this PR's CI signal reproducible.
-          npm install -g "@copilotkit/aimock@^1.14.3" --ignore-scripts
+          npm install -g "@copilotkit/aimock@^1.16.4" --ignore-scripts
           # Invoke the installed global binary directly rather than `npx`.
-          # `npx @copilotkit/aimock@^1.14.3` re-resolves the spec against the
+          # `npx @copilotkit/aimock@^1.16.4` re-resolves the spec against the
           # registry and MAY re-fetch a package even when an identical global
           # install exists — which would defeat `--ignore-scripts` on the
           # npm-install step above (npx's transient install does not inherit