agent_sockets: address argus 🟡 on #832 (doc attribution + drop unused arg)

argus on PR #832:
- 🟡 spawn_poll was inserted BETWEEN write's closing doc and the
  pub fn write line; rust treated the consecutive /// as one block,
  so spawn_poll inherited write's tail and write ended up with no
  closing doc. moved spawn_poll AFTER write to fix attribution.
- 🟡 spawn_poll(coord) took Arc<Coordinator> just to drop it
  immediately. dropped the param; main.rs call site now just
  agent_sockets::spawn_poll().

no functional change. 10 tests still pass.

hive-c0re/src/main.rs

@@ -261,7 +261,7 @@ async fn cmd_serve(
     // idempotent so steady-state cost is one stat per agent per
     // tick. closes atlas's #813 concern that agents in the JSON
     // would 502 the gateway until they actually opt in.
-    agent_sockets::spawn_poll(coord.clone());
+    agent_sockets::spawn_poll();
     // Reminder scheduler: drains due reminders + handles
     // file_path payload persistence. See reminder_scheduler.rs.
     reminder_scheduler::spawn(coord.clone());