Add edge gateway broker configurations and session management routes

- Add broker-related configuration classes (`broker_url`, `public_broker_url`, `auth_mode`, `shared_secret`) to support edge gateway functionality.
- Enhance `SelfserveRoute` with routes for managing self-serve wash sessions, including session listing, detail retrieval, and forced lane stop.
- Update unit tests to validate new configuration handling, session routes, and OpenAPI endpoint coverage.
- Include default environment variables for broker settings in `docker-compose.example.yml`.

docker-compose.yml

@@ -86,6 +86,7 @@ services:
       dockerfile: services/edge-broker/Dockerfile
     container_name: edge-broker
     environment:
+      EDGE_AUTH_MODE: ${EDGE_AUTH_MODE:-manager}
       EDGE_MANAGER_URL: ${EDGE_MANAGER_URL:-http://caddy}
       EDGE_BROKER_SHARED_SECRET: ${EDGE_BROKER_SHARED_SECRET:-truckwash-edge-dev}
     labels: