agent page: inbox view of last 30 messages addressed to this agent

new wire request AgentRequest::Recent { limit } / ManagerRequest::Recent
(plus matching responses with Vec<InboxRow>). InboxRow moved to
hive-sh4re so it lives on both surfaces without an internal-to-wire
conversion. host-side dispatch in agent_server / manager_server
calls broker.recent_for(name, limit).

per-agent web_ui /api/state grew an inbox: Vec<InboxRow> populated
via the same per-agent socket (best-effort; transport failure
returns empty). frontend renders as a collapsible <details> section
between the state row and the terminal — fmt timestamp / from /
body in a tight grid, capped at 16em scrollable. only visible when
there are rows.

hive-ag3nt/src/bin/hive-ag3nt.rs

@@ -139,7 +139,7 @@ async fn serve(
                 turn::emit_turn_end(&bus, &outcome);
             }
             Ok(AgentResponse::Empty) => {}
-            Ok(AgentResponse::Ok | AgentResponse::Status { .. }) => {
+            Ok(AgentResponse::Ok | AgentResponse::Status { .. } | AgentResponse::Recent { .. }) => {
                 tracing::warn!("recv produced unexpected response kind");
             }
             Ok(AgentResponse::Err { message }) => {