Add screen activity signaler to prevent display sleep

- Added signal_screen_activity() method to SignagePlayer class
- Runs every 20 seconds automatically
- Also triggered on any touch/user input events

Multiple methods used to keep display awake:
- xset s reset - Resets screensaver timer
- xset dpms force on - Forces display on
- xdotool - Subtle mouse movement to trigger activity

This complements the system-level power management:
- Works alongside display power management settings
- Non-blocking and non-critical (fails gracefully)
- Signals every 20 seconds + on user input
- Prevents display from sleeping during playback

Screen should now remain active throughout media playback.

src/main.py

@@ -910,6 +910,8 @@ class SignagePlayer(Widget):
         self.schedule_hide_controls()
         # Start heartbeat monitoring
         Clock.schedule_interval(self.update_heartbeat, 10)  # Update every 10 seconds
+        # Start screen activity signaler (keep display awake)
+        Clock.schedule_interval(self.signal_screen_activity, 20)  # Signal every 20 seconds
 
     def _update_size(self, instance, value):
         self.size = value
@@ -925,6 +927,31 @@ class SignagePlayer(Widget):
         except Exception as e:
             Logger.warning(f"SignagePlayer: Failed to update heartbeat: {e}")
 
+    def signal_screen_activity(self, dt):
+        """Signal screen activity to prevent power saving/sleep
+        
+        Uses multiple methods to keep display awake:
+        1. xset s reset - Reset screensaver timeout
+        2. xset dpms force on - Force display on
+        3. xdotool - Move mouse to trigger activity
+        """
+        try:
+            # Method 1: Reset screensaver timer using xset
+            os.system('xset s reset 2>/dev/null')
+            
+            # Method 2: Force display on
+            os.system('xset dpms force on 2>/dev/null')
+            
+            # Method 3: Move mouse slightly (subtle, user won't notice)
+            if os.system('xdotool mousemove_relative 1 1 2>/dev/null') == 0:
+                os.system('xdotool mousemove_relative -1 -1 2>/dev/null')
+                
+            Logger.debug("SignagePlayer: Screen activity signal sent (display kept awake)")
+            
+        except Exception as e:
+            Logger.debug(f"SignagePlayer: Screen activity signal failed (non-critical): {e}")
+            # Non-critical - continue if this fails
+
     def initialize_player(self, dt):
         """Initialize the player - load config and start playlist checking"""
         Logger.info("SignagePlayer: Initializing player...")
@@ -1502,12 +1529,14 @@ class SignagePlayer(Widget):
         self.ids.status_label.opacity = 1
 
     def on_touch_down(self, touch):
-        """Handle touch - show controls"""
+        """Handle touch - show controls and signal screen activity"""
+        self.signal_screen_activity(0)  # Keep display awake on user input
         self.show_controls()
         return super(SignagePlayer, self).on_touch_down(touch)
 
     def on_touch_move(self, touch):
-        """Handle touch move - show controls"""
+        """Handle touch move - show controls and signal screen activity"""
+        self.signal_screen_activity(0)  # Keep display awake on user input
         self.show_controls()
         return super(SignagePlayer, self).on_touch_move(touch)