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.h

@@ -137,6 +137,7 @@ public:
   void gotoSettingsScreen();
   void gotoQuickMsgScreen();
   void openContactDM(const ContactInfo& ci);
+  void shareToMessage(const char* text);   // open Messages pre-loaded to share `text`
   int  getRecentDMContacts(uint8_t out[][NodePrefs::FAVOURITE_PREFIX_LEN], int max) const;
   void gotoToolsScreen();
   void gotoRingtoneEditor(int slot = 0);