node: source connection start/activity timestamps from the peer machine

The connection leg's started_at and last_activity duplicated the peer
machine's own connection-state copy. Make the machine copy the sole live
telemetry and timeout carrier: re-stamp it with the leg's provenance when
the leg is attached at handshake start (the msg1-prep clock, not the earlier
dial-time constructor value) and mirror the completion touch, then delete the
leg's last_activity/touch accessors and source the connection-row projection,
show_connections, and the timeout readers from the machine. Byte-identical
for all normal paths.

src/control/queries.rs

@@ -1308,8 +1308,8 @@ pub fn show_connections(node: &Node) -> Value {
                 "link_id": conn.link_id().as_u64(),
                 "direction": format!("{}", conn.direction()),
                 "handshake_state": node.connection_handshake_state(conn.link_id()),
-                "started_at_ms": conn.started_at(),
-                "idle_ms": now.saturating_sub(conn.last_activity()),
+                "started_at_ms": node.connection_started_at(conn.link_id()),
+                "idle_ms": now.saturating_sub(node.connection_last_activity(conn.link_id())),
                 "resend_count": node.connection_resend_count(conn.link_id()),
             });