chore: add CI job to validate ui-patterns exports (#47408)

## Problem

`ui-patterns` exports its components under a subpath (see its
`package.json`). This is easy to forget when adding a new component.

## Solution

Add a CI job that validate the exports are corrects

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Added a new “Validate exports” step to the UI patterns pipeline to
ensure generated exports remain in sync.
* When discrepancies are detected, the workflow outputs the diff and
fails immediately to prevent stale artifacts.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Ivan Vasilov <vasilov.ivan@gmail.com>

.github/workflows/ui-patterns-tests.yml

@@ -40,5 +40,13 @@ jobs:
       - name: Install deps
         run: pnpm install --frozen-lockfile
 
+      - name: Validate exports
+        run: |
+          pnpm --filter ui-patterns gen:exports
+          if ! git diff --ignore-space-at-eol --exit-code --quiet packages/ui-patterns/package.json then
+            echo "Detected uncommitted changes after build. Run pnpm --filter ui-patterns gen:exports to fix it."
+            git diff
+            exit 1
+          fi
       - name: Run tests
         run: pnpm run test:ui-patterns