refactor(ci): replace pnpm/action-setup with Nix in release workflow

- Use local setup-nix action instead of pnpm/action-setup
- Run pnpm commands through nix develop for consistent tooling
- Keep setup-node and registry configuration for npm publish

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ryoppippi

.github/workflows/release.yaml

@@ -30,7 +30,8 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
 
-      - uses: pnpm/action-setup@41ff72655975bd51cab0327fa583b6e92b6d3061 # v4.2.0
+      - name: Setup Nix
+        uses: ./.github/actions/setup-nix
 
       - name: Setup Node.js for npm
         uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f # v6.1.0
@@ -41,7 +42,7 @@ jobs:
           registry-url: "https://registry.npmjs.org"
 
       - name: 💫 Install dependencies
-        run: pnpm install --frozen-lockfile
+        run: nix develop --command pnpm install --frozen-lockfile
 
       - name: 🚀 Publish package
-        run: pnpm publish --access public --no-git-checks
+        run: nix develop --command pnpm publish --access public --no-git-checks