fix(l2): a dot per DM send, lists that notice every change, the LED lit only on TX

- A pending DM shows a dot per send, as on the L1. The thread is read from
  the SD archive, which a resend never updated: it does now, and the
  thread's signature and patch state count the attempt.
- Nearby redraws when a node goes live, changes type or the units change;
  the scan popup when a name or the remote SNR arrives.
- The user LED is active high: it was lit all the time and went dark
  while transmitting.
- Sim hooks "dm" and "send" for testing a DM thread.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-core/MessageHistory.h

@@ -460,6 +460,9 @@ public:
         e.ack_tag         = expected_ack;   // each attempt has a distinct ACK CRC
         e.ack_deadline_ms = now + est_timeout + 4000;
         e.resends_left--;
+#ifdef HIST_ARCHIVE
+        if (_arc) _arc->dmUpdate(e);        // the thread is read from it: a dot per send
+#endif
       } else {
         failDm(e);                          // couldn't compose/send — give up
       }