Add autostart functionality and power management for Raspberry Pi

- Enhanced install.sh with comprehensive autostart workflow:
  * XDG autostart entry (desktop environment)
  * systemd user service (most reliable)
  * LXDE autostart support (Raspberry Pi OS)
  * Cron fallback (@reboot)
  * Terminal mode enabled for debugging

- Added Raspberry Pi power management features:
  * Disable HDMI screen blanking
  * Prevent CPU power saving (performance mode)
  * Disable system sleep/suspend
  * X11 screensaver disabled
  * Display power management (DPMS) disabled

- Fixed sudo compatibility:
  * Properly detects actual user when run with sudo
  * Correct file ownership for user configs
  * systemctl --user works correctly

- Player launches in terminal for error visibility
- Autostart configured to use start.sh (watchdog with auto-restart)

.start-player-cron.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+# Wait for desktop environment to be ready
+sleep 10
+
+# Start the player
+cd "/home/pi/Desktop/Kiwy-Signage" && bash start.sh