ci(release): use setup-nix action with nix develop

Use the setup-nix composite action for consistent Nix setup across
workflows, while still using nix develop for commands to leverage the
full devShell environment.

- Replace direct install-nix-action with setup-nix composite action
- Add skip-uv-sync since nix develop handles dependencies
- Keep nix develop --command for build commands

Author: ryoppippi

.github/workflows/release.yaml

@@ -28,7 +28,7 @@ jobs:
         if: ${{ steps.release.outputs.release_created }}
         uses: ./.github/actions/setup-nix
         with:
-          skip-mock-server: "true"
+          skip-uv-sync: "true"
 
       - name: Update version in __init__.py
         if: ${{ steps.release.outputs.release_created }}