Add screen keep-alive functionality to prevent display sleep

- Created .keep-screen-alive.sh wrapper script with multiple methods:
  * systemd-inhibit (primary - prevents OS-level sleep/suspend)
  * xset commands (prevents X11 screensaver)
  * Mouse movement (prevents idle timeout)

- Added screen-keepalive.service systemd unit:
  * Runs xset s reset every 30 seconds
  * Auto-restarts on failure
  * Integrated with graphical session

- Multiple layers of screen protection:
  * HDMI blanking disabled
  * CPU power saving disabled
  * System sleep/suspend disabled
  * X11 screensaver disabled
  * DPMS (Display Power Management) disabled
  * Display forced on periodically

Screen will now remain active while player is running, preventing lockups or blank screens during playback.

.keep-screen-alive.sh

@@ -0,0 +1,54 @@
+#!/bin/bash
+# Keep-screen-alive wrapper for player
+# Prevents screen from locking/turning off while player is running
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+# Function to keep screen awake
+keep_screen_awake() {
+    while true; do
+        # Move mouse slightly to prevent idle
+        if command -v xdotool &> /dev/null; then
+            xdotool mousemove_relative 1 1
+            xdotool mousemove_relative -1 -1
+        fi
+        
+        # Disable DPMS and screensaver periodically
+        if command -v xset &> /dev/null; then
+            xset s reset
+            xset dpms force on
+        fi
+        
+        sleep 30
+    done
+}
+
+# Function to inhibit systemd sleep (if available)
+inhibit_sleep() {
+    if command -v systemd-inhibit &> /dev/null; then
+        # Run player under systemd inhibit to prevent sleep
+        systemd-inhibit --what=sleep --why="Signage player running" \
+            bash "$SCRIPT_DIR/start.sh"
+        return $?
+    fi
+    return 1
+}
+
+# Try systemd inhibit first (most reliable)
+if inhibit_sleep; then
+    exit 0
+fi
+
+# Fallback: Start keep-alive in background
+keep_screen_awake &
+KEEPALIVE_PID=$!
+
+# Start the player
+cd "$SCRIPT_DIR"
+bash start.sh
+PLAYER_EXIT=$?
+
+# Kill keep-alive when player exits
+kill $KEEPALIVE_PID 2>/dev/null || true
+
+exit $PLAYER_EXIT