Outbound WebSocket support for server-to-server realtime integrations

Convex actions can call external services over HTTP, but there is currently no way for Convex backend code to establish and maintain an outbound WebSocket connection to an external service. This limits an important class of backend integrations where a Convex deployment needs to subscribe to and process a live stream of events from another system, rather than making one-shot request/response calls. Real-world examples include market-data and pricing feeds, logistics/dispatch and location streams, inventory/order-status and operations events, device or network telemetry, fraud/risk streams, and realtime agent or voice sessions. In these systems, the backend often needs a persistent bidirectional connection for subscription, heartbeats, incremental updates, and reconnect handling, then needs to write the streamed state back into the application data model. Please add first-class outbound WebSocket support for backend functions so Convex can coordinate long-lived external realtime sessions, not just request/response HTTP workflows.