Integrate wave-based scaling system with WHOOSH server

- Add scaling system components to server initialization
- Register scaling API and assignment broker routes
- Start bootstrap pool manager in server lifecycle
- Add graceful shutdown for scaling controller
- Update API routing to use chi.Router instead of gorilla/mux
- Fix Docker API compatibility issues
- Configure health gates with placeholder URLs for KACHING and BACKBEAT

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

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

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/golang-jwt/jwt/v5 v5.3.0
 	github.com/golang-migrate/migrate/v4 v4.17.0
 	github.com/google/uuid v1.6.0
+	github.com/gorilla/mux v1.8.1
 	github.com/jackc/pgx/v5 v5.5.2
 	github.com/kelseyhightower/envconfig v1.4.0
 	github.com/rs/zerolog v1.32.0