chore(cloud-agent-next): raise SandboxSmall max_instances to 400 (#2845)

Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>

Author: kilo-code-bot[bot]

services/cloud-agent-next/wrangler.jsonc

@@ -149,7 +149,7 @@
       "image_vars": {
         "KILOCODE_CLI_VERSION": "7.1.23",
       },
-      "max_instances": 100,
+      "max_instances": 400,
       "rollout_active_grace_period": 1800,
     },
   ],