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.

GDD.md

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+## **Chain Reaction - Game Design Document**
+
+### **Core Concept**
+
+Players click once to create a static explosion that destroys floating circles. The goal is to clear the screen with one strategic click, triggering chain reactions of destruction.
+
+### **Gameplay Mechanics**
+
+**Primary Mechanic**:
+
+- Click anywhere to create explosion at position
+- Explosions destroy circles within radius
+- Destroyed circles trigger secondary explosions (chain reaction)
+- Game ends when all circles are destroyed or time expires
+
+**Circle Properties**:
+
+- Random radii (10-50px)
+- Random alpha transparency (0.3-1.0)
+- Random colors (pastel palette)
+- Physics: Smooth movement, collision detection
+
+**Explosion Mechanics**:
+
+- Static explosion at click position
+- Explosion radius = 100px (tunable)
+- Chain reaction: Destroyed circles explode after 0.1s delay
+- Secondary explosions have 50% smaller radius
+
+### **Core Loop**
+
+**30-second gameplay cycle**:
+
+- Start with 20-30 circles
+- Player clicks strategically to create chain reactions
+- Game ends when all circles destroyed OR time runs out (30 seconds)
+- Win condition: Clear screen before time expires
+
+### **Scoring System**
+
+- Points = circles destroyed × multiplier
+- Multiplier increases with consecutive chain reactions (1x, 2x, 4x, 8x...)
+- Bonus points for clearing all circles in single click
+
+### **Visual Design**
+
+**Art Style**: Minimalist circles with:
+
+- Pastel color palette (blues, purples, pinks)
+- Alpha transparency (0.3-1.0)
+- Smooth movement animations
+- Particle effects on destruction
+
+**UI Elements**:
+
+- Score display
+- Timer countdown
+- "Chain Reaction" indicator
+- Restart button
+
+### **Technical Requirements**
+
+**Spatial Partitioning**: Grid-based system for efficient collision detection
+**Performance**: Handle 500+ circles with 60fps target
+**Physics**: Smooth movement, realistic collision response
+
+### **Game States**
+
+1. **Menu**: Start screen, instructions, high score
+2. **Playing**: Main gameplay loop
+3. **GameOver**: Score display, restart option
+
+### **Implementation Roadmap**
+
+1. Basic window + circle generation (5min)
+2. Click detection + explosion mechanics (10min)
+3. Chain reaction logic + destruction system (15min)
+4. Scoring + game states (10min)
+5. Polish + optimization (20min)
+
+### **Optional Enhancements**
+
+- Power-ups (larger explosions, slower circles)
+- Different circle types (fast/slow, larger/smaller)
+- Time pressure mechanic
+- High score system with local persistence