feat(nav): share a waypoint as a message

Waypoints list → Hold Enter → Send hands the point to the Messages screen
as "[WAY]<lat>,<lon> <label>" (same text format geo::parseLatLon already
reads). The user picks a contact or channel, the text lands prefilled in
the keyboard to confirm/edit, then sends — closing the loop with the
Navigate / Save waypoint actions on the receiving end.

- QuickMsgScreen: share-compose mode (startShare/beginShareCompose). Picking
  a recipient jumps straight to the prefilled keyboard; cancel returns home;
  afterSend clears the mode.
- UITask::shareToMessage hands off from TrailScreen to the Messages screen.
- TrailScreen: "Send" added to the waypoint Rename/Delete popup; builds the
  [WAY] payload at the {loc} precision (5 dp).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/TrailScreen.h

@@ -119,13 +119,22 @@ public:
             _wp_kb.begin(_task->waypoints().at(wi).label, WAYPOINT_LABEL_LEN - 1);
             _kb_active = true;
           }
-        } else {                                          // Delete
+        } else if (sel == 1) {                            // Delete
           if (wi >= 0 && wi < _task->waypoints().count()) {
             _task->waypoints().remove(wi);
             _task->saveWaypoints();
             if (_wp_sel >= wpListCount()) _wp_sel = wpListCount() - 1;
             if (_wp_sel < 0) _wp_sel = 0;
           }
+        } else {                                           // Send (share in a message)
+          if (wi >= 0 && wi < _task->waypoints().count()) {
+            const Waypoint& w = _task->waypoints().at(wi);
+            double lat = w.lat_1e6 / 1000000.0, lon = w.lon_1e6 / 1000000.0;
+            char text[80];
+            if (w.label[0]) snprintf(text, sizeof(text), WAYPOINT_MSG_TAG "%.5f,%.5f %s", lat, lon, w.label);
+            else            snprintf(text, sizeof(text), WAYPOINT_MSG_TAG "%.5f,%.5f", lat, lon);
+            _task->shareToMessage(text);   // hands off to the Messages screen
+          }
         }
       }
       return true;
@@ -147,9 +156,10 @@ public:
       if (c == KEY_ENTER && n > 0)          { _wp_mode = WP_NAV; return true; }
       // Rename/Delete apply to saved waypoints only — not the Trail-start row.
       if (c == KEY_CONTEXT_MENU && !selIsStart() && wpIndex() < _task->waypoints().count()) {
-        _wp_ctx.begin("Waypoint", 2);
+        _wp_ctx.begin("Waypoint", 3);
         _wp_ctx.addItem("Rename");
         _wp_ctx.addItem("Delete");
+        _wp_ctx.addItem("Send");
         return true;
       }
       return true;