docker: read the resolver file a container really uses (hq issue 348)

On 2026-10-09 the control node's route-proxy failed every lookup against 10.10.0.1 alone for twenty
minutes while the machine's file listed both mesh resolvers; its copy lives under the runtime's
root-only directory and no tool read it. docker_resolv_conf reads /etc/resolv.conf as the container
sees it through the runtime's archive (docker cp, no exec), parses it, and says whether it lists the
same resolvers as the machine.

modules/docker/module.json

@@ -18,6 +18,7 @@
   "tools": [
     "docker_list",
     "docker_inspect",
+    "docker_resolv_conf",
     "docker_logs",
     "docker_secrets_in_logs",
     "docker_secrets_in_events",
@@ -38,6 +39,11 @@
     "docker_problems",
     "docker_ports"
   ],
+  "replaces": {
+    "docker_resolv_conf": [
+      "docker exec cat /etc/resolv.conf"
+    ]
+  },
   "resources": [
     {
       "id": "package",