feat(cloud-agent-next): enable tracing in observability config

Update the observability block in wrangler.jsonc to enable traces
and persistent logs with head_sampling_rate=1, while keeping the
top-level observability.enabled flag false so the full pipeline
can be activated in a controlled rollout.

Author: kilo-code-bot[bot]

cloud-agent-next/wrangler.jsonc

@@ -18,7 +18,19 @@
     "ip": "0.0.0.0",
   },
   "observability": {
-    "enabled": true,
+    "enabled": false,
+    "head_sampling_rate": 1,
+    "logs": {
+      "enabled": true,
+      "head_sampling_rate": 1,
+      "persist": true,
+      "invocation_logs": true,
+    },
+    "traces": {
+      "enabled": true,
+      "persist": true,
+      "head_sampling_rate": 1,
+    },
   },
   "logpush": true,
   "routes": [