feat: Implement background shader and visual effects

- Added a new WGSL shader for background rendering with volumetric fog effects.
- Created components for game entities including Circle, Velocity, Explosion, and ChainReaction.
- Introduced game state management with GameState enum and LevelState resource.
- Implemented event system for explosion requests and circle destruction notifications.
- Developed plugins for game logic, input handling, movement, reactions, scoring, and UI.
- Configured game settings through GameConfig resource with adjustable parameters.
- Enhanced UI with configuration options and game over screens.
- Integrated spatial grid for efficient collision detection and explosion handling.

src/events.rs

@@ -0,0 +1,11 @@
+use bevy::prelude::*;
+
+#[derive(Event)]
+pub struct ExplosionRequest {
+    pub pos: Vec2,
+}
+
+#[derive(Message)]
+pub struct CircleDestroyedMessage {
+    pub pos: Vec2,
+}