fix(beszel): improve live subscription error handling and cleanup

- Surface subscription errors in useLiveStats via onError + error state
- Show error UI in live mode when SSE connection fails
- Abort SSE reader on subscribeTopic failure instead of silent log
- Guard mock realtime against pre-aborted signal to prevent interval leak
- Remove dead includeDocker from subscription input schema

packages/integrations/src/beszel/beszel-integration.ts

@@ -283,7 +283,8 @@ export class BeszelIntegration extends Integration {
         if (!clientId && typeof parsed.clientId === "string") {
           clientId = parsed.clientId;
           this.subscribeTopic(clientId, systemId, session.token).catch((err) => {
-            logger.warn("Failed to subscribe to rt_metrics topic", { error: err });
+            logger.warn("Failed to subscribe to rt_metrics topic, aborting SSE", { error: err });
+            reader.cancel().catch(() => {});
           });
           return;
         }

packages/integrations/src/mock/data/beszel.ts

@@ -350,12 +350,13 @@ export class BeszelMockService {
       };
       onMessage({ stats: record, containerStats: null });
     };
+    if (signal.aborted) return;
     await new Promise<void>((resolve) => {
       const interval = setInterval(emit, 1000);
       signal.addEventListener("abort", () => {
         clearInterval(interval);
         resolve();
-      });
+      }, { once: true });
     });
   }