Fix infinite recursion when restarting player with empty playlist

- Added empty playlist guard in play_current_media() to return
  early instead of calling restart_playlist()
- Added empty playlist guard in restart_playlist() to return
  early instead of calling play_current_media()
- Wrapped SettingsPopup content in ScrollView so fields
  are not cut off on smaller screens

src/main.py

@@ -1299,7 +1299,11 @@ class SignagePlayer(Widget):
             Logger.debug(f"SignagePlayer: Skipping play_current_media - player is paused")
             return
             
-        if not self.playlist or self.current_index >= len(self.playlist):
+        if not self.playlist:
+            Logger.warning("SignagePlayer: Cannot play - playlist is empty")
+            return
+        
+        if self.current_index >= len(self.playlist):
             # End of playlist, restart
             self.restart_playlist()
             return
@@ -2068,6 +2072,10 @@ class SignagePlayer(Widget):
 
     def restart_playlist(self):
         """Restart playlist from beginning"""
+        if not self.playlist:
+            Logger.warning("SignagePlayer: Cannot restart - playlist is empty")
+            return
+        
         Logger.info("SignagePlayer: Restarting playlist")
         
         # Send restart feedback asynchronously (non-blocking)