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/UITask.cpp

@@ -1325,6 +1325,11 @@ void UITask::openContactDM(const ContactInfo& ci) {
   setCurrScreen(quick_msg);
 }
 
+void UITask::shareToMessage(const char* text) {
+  ((QuickMsgScreen*)quick_msg)->startShare(text);
+  setCurrScreen(quick_msg);
+}
+
 int UITask::getRecentDMContacts(uint8_t out[][NodePrefs::FAVOURITE_PREFIX_LEN], int max) const {
   return ((QuickMsgScreen*)quick_msg)->getRecentDMContacts(out, max);
 }