fix: add npm registry auth token for UI build in CI

The Build UI step ran npm ci without authenticating to the Gitea npm
registry, causing @cameleer/design-system to fail to resolve. Add
REGISTRY_TOKEN to .npmrc before npm ci.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -53,8 +53,11 @@ jobs:
       - name: Build UI
         working-directory: ui
         run: |
+          echo '//gitea.siegeln.net/api/packages/cameleer/npm/:_authToken=${REGISTRY_TOKEN}' >> .npmrc
           npm ci
           npm run build
+        env:
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Build and Test
         run: mvn clean verify -DskipITs --batch-mode