FLIPPIX OS v0.5.1 — Boot Splash & Backlight Timeout

Hardware-tested display and power-saving microrelease for Flipper Zero. Adds the custom 128x64 FLIPPIX OS boot splash at maximum brightness, restores the configured brightness after three seconds, and adds backlight auto-off choices for 30 seconds, 1 minute, 2 minutes, or Never. Activity from physical buttons, BLE controls, or console output wakes the backlight and resets its timer. The LCD, OS, USB CDC, and microSD remain active while the backlight is off.