fix: messages that arrive while asleep or locked stay unread

A conversation left open under the lock screen or a dark display no longer
counts as read: the counters and the lock screen's tally go up, and on
waking (L2: on unlocking) the conversation reopens on its first unread
under the "New" line, a typed draft kept.

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

examples/companion_radio/ui-lvgl/UITask.h

@@ -131,6 +131,8 @@ public:
   void simCompose(const char* text);    // the open thread's field: this text, keyboard up
   void simDm();                         // the first chat contact's thread
   void simUnread();                     // read and new messages to open on
+  void simSleep(bool on) { if (on) sleep(); else wake(); }
+  void simLock(bool on) { if (on) lockScreen(); else unlockScreen(); }
   void simSend() { sendFromCompose(); } // the field, sent
   // Navigation map (NavMap.h)
   void navTargetsPopup();
@@ -427,6 +429,7 @@ private:
   void refreshNode();
   void buildThread();
   void threadOpenAt(int first);
+  void reopenThreadIfUnread();
   void refreshThread();
   void refreshThreadAges();
   uint32_t threadSignature() const;