Add new assets and implement minimap functionality

- Added new image assets for game over screens: `game_over_dead_bg.png`, `game_over_victory_bg.png`, and their respective Aseprite files.
- Introduced a new `Minimap` class to manage torch placement and rendering on the minimap.
- Implemented methods for adding and removing torches, updating the grid area, and drawing the minimap based on the current state of the game.
- Enhanced the minimap display with color coding for walls, empty spaces, and torches.

game_over/scene.rb

@@ -8,7 +8,7 @@ class GameOver < Scene
     super
     @font = Gosu::Font.new(32, name: "assets/fonts/tn.ttf")
     @selected_index = 0
-    @bg_image = Gosu::Image.new("assets/images/game_over_bg.png", retro: true)
+    @bg_image = Gosu::Image.new("assets/images/game_over_#{$is_dead ? 'dead' : 'victory'}_bg.png", retro: true)
     @last_mouse_pos = nil
   end