fix: handle ERR_NETWORK_CHANGED from Docker network changes

- Add retry logic for transient network errors in API client
- Retry up to 2 times with exponential backoff on network errors
- Reduce session polling from 10s to 30s to decrease error frequency
- Handle 502/503/504 gateway errors with retries as well

apps/web/src/components/app-shell.tsx

@@ -58,10 +58,10 @@ export const AppShell = () => {
 
   useEffect(() => {
     void loadSessions();
-    // Poll every 10 seconds
+    // Poll every 30 seconds (reduced from 10s to avoid ERR_NETWORK_CHANGED from Docker network changes)
     const interval = setInterval(() => {
       void loadSessions();
-    }, 10000);
+    }, 30000);
     return () => clearInterval(interval);
   }, [loadSessions]);