Revert CI workaround now that build-essential is installed

- Restore bufferutil as regular dependency for WebSocket performance
- Remove --no-optional flag from npm ci
- Self-hosted runners now have proper C++ build tools installed

This enables full native module support and optimal WebSocket performance.

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

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

.forgejo/workflows/build.yml

@@ -19,7 +19,7 @@ jobs:
         run: rm -rf .next
 
       - name: Install dependencies
-        run: npm ci --no-optional
+        run: npm ci
 
       - name: Run type check
         run: npm run type-check