feat: add customizable PyUI screensaver

[vigstudio]

Summary

Adds a full screensaver customization system to PyUI with background images, GIF support, RGB color picker, visual widget layout editor, battery styles, and bundled fonts.

Features

• Background image/GIF picker - scans user folder, theme folder, and default
• RGB color picker - R/G/B sliders with live preview (A save, B cancel)
• Visual widget layout editor - D-pad move, L1/R1 size, L2/R2 palette color, START RGB, Y font/battery style, X toggle, SELECT widget switch
• 5 battery styles - percent, blocks, bar, pill, segments
• 8 bundled fonts - PressStart2P, VT323, Silkscreen, PixelifySans, Orbitron, Audiowide, BungeeShade, EmilysCandy
• Overlay - configurable opacity/color/blur
• GIF animation - frame-by-frame rendering via IMG_LoadAnimation (no texture cache to save RAM)
• Render target fix - screensaver renders to render_canvas then Display.present() (no bars)
• Top/bottom bar hidden during screensaver via _present_without_bars()
• Wake input does not pass through to menus
• In-game guard - _game_running flag prevents screensaver during gameplay

Files Changed

• New: display/screensaver.py (444 lines) - ScreenSaver class
• New: menus/settings/screensaver_settings_menu.py (450 lines) - Settings UI
• New: hemes/screensaver.png - Default retro synthwave background
• New: onts/ - 8 TTF files
• New: docs/pyui-screensaver-customization.md - Install/usage docs
• Modified: controller/controller.py - idle timeout, _try_start_screensaver
• Modified: display/display.py - blank_screen, restore_from_blank, set_page_bg guard
• Modified: hemes/theme.py - screensaver getter methods
• Modified: utils/py_ui_config.py - get_screensaver_timeout_sec
• Modified: �iews/*.py - screensaver render guards
• Modified: menus/games/in_game_menu_listener.py - _game_running flag
• Modified: menus/settings/extra_settings_menu.py - screensaver menu entry

Device Verified

• CPU low, PyUI RSS ~91-105MB, no errors in log after fixes
• Screensaver activates after idle timeout, wakes on any input
• In-game flag prevents screensaver during gameplay

Docs

• docs/pyui-screensaver-customization.md - full install and usage guide
• docs/pyui-screensaver-style-preview.png - style preview contact sheet