fix(gate): 600s query-phase client timeout

The dashboard seven-day surface pages all 12.1M sketch rows to completion
per the read contract's percentile path; on 2 vCPUs that takes over the
former 120s client timeout (traffic: 10.6s, service-map: 15.6s, dashboard:
>120s in run 6). The contract binds completeness and honesty, not query
latency; the timeout is harness plumbing and durations are recorded in the
report.

Author: aksOps

test/gate/gate.config.json

@@ -179,7 +179,7 @@
         }
       }
     ],
-    "timeout_sec": 120
+    "timeout_sec": 600
   },
   "thresholds": {
     "sustained_hours": 3,