refactor: use PopupMenu in keyboard and context menus, fix bugs

- KeyboardWidget: replace inline placeholder overlay with PopupMenu
- UITask QuickMsgScreen: replace inline CONTACT_PICK/CHANNEL_PICK context
  menus with PopupMenu; notif label stored in _ctx_notif_item at open time
- BotScreen: clear placeholder list for trigger field (expansion tokens
  would never match incoming literal text)
- MsgExpand: fix APPEND macro off-by-one (oi+_l < out_len-1 → < out_len)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/BotScreen.h

@@ -175,8 +175,11 @@ public:
         max     = sizeof(_prefs->bot_reply_ch) - 1;
       }
       _kb.begin(initial, max);
-      if (_sel != 2)  // trigger field doesn't support sensor placeholders
+      if (_sel == 2) {
+        _kb._ph_count = 0;  // trigger is literal text — placeholders never match incoming msgs
+      } else {
         kbAddSensorPlaceholders(_kb, &sensors);
+      }
       return true;
     }
     return false;