fix(release): use correct package name 'llmx' instead of '@valknar/llmx'

The build_npm_package.py script only accepts specific package choices:
'llmx', 'llmx-responses-api-proxy', 'llmx-sdk'. The scoped package name
'@valknar/llmx' is not a valid choice.

The package name 'llmx' is the correct identifier used internally by the
build system, which then produces the scoped npm package.

.github/workflows/rust-release.yml

@@ -445,7 +445,7 @@ jobs:
         run: |
           ./scripts/stage_npm_packages.py \
             --release-version "${{ steps.release_name.outputs.name }}" \
-            --package @valknar/llmx
+            --package llmx
 
       - name: Create GitHub Release
         uses: softprops/action-gh-release@v2