Make ckpool client resilient to warm-up EOFs

The stratifier can accept a connection and close it without
writing a response during early startup — the refresh loop
then logs 'ckpool poolstats failed: read len: EOF' on every
tick until the stratifier is ready, which is noisy and looks
like a real fault.

- client.Send retries once after 200ms if the server closed
  the connection before any bytes were read (io.EOF anywhere
  in the wrapped chain).
- Aggregator tracks a ckFailStreak counter: first two
  consecutive failures log at DEBUG, third and beyond escalate
  to WARN. Successful refreshes reset the streak.

ui/package.json

@@ -16,6 +16,6 @@
     "svelte": "^5.0.0",
     "svelte-check": "^4.0.0",
     "typescript": "^5.6.0",
-    "vite": "^5.4.0"
+    "vite": "^6.0.0"
   }
 }