Custom Game Logos and Refined Menus

Changes

• Added per-game Game Logo customization in Game Details / Appearance, with support for local logo art, online logo search, and resizing.
• Redesigned the game menu to open beside the selected game, with smoother folder submenus and new option icons.
• Folder previews in the Installed Library now follow the selected Square or Poster icon style.
• Fixed poster fallback artwork appearing before the requested poster finished loading, and removed redundant loading dots from Steam library poster grids.
• Cached decoded default posters to reduce repeated image processing while browsing the library.