ci: gate release publish on environment approval with Discord notice (#1571)

## Summary
- Add `environment: release` to the `Release` job so npm publishing is
gated by a manual approval on the `release` environment.
- Introduce a `request-approval` job that fires before the `Release` job
and posts a Discord message with a link to the workflow run, so
reviewers know an approval is waiting.

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

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Boshen

.github/workflows/release.yml

@@ -60,9 +60,19 @@ jobs:
       version: ${{ needs.prepare.outputs.version }}
       cache-key: release
 
-  Release:
+  request-approval:
     runs-on: ubuntu-latest
     needs: [prepare, build-rust]
+    steps:
+      - uses: tsickert/discord-webhook@b217a69502f52803de774ded2b1ab7c282e99645 # v7.0.0
+        with:
+          webhook-url: ${{ secrets.DISCORD_RELEASES_WEBHOOK_URL }}
+          content: 'Requesting approval: ${{ github.server_url }}/${{ github.repository }}/actions/workflows/release.yml'
+
+  Release:
+    runs-on: ubuntu-latest
+    environment: release
+    needs: [prepare, build-rust, request-approval]
     permissions:
       contents: write
       packages: write