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.

README.md

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+# Chain Reaction
+
+A minimalist physics-based puzzle game where strategic clicks create explosive chain reactions. Clear the screen with one perfect click!
+
+![License](https://img.shields.io/badge/license-MIT-blue.svg)
+
+## About
+
+Chain Reaction is a fast-paced arcade game built with Rust and Bevy. Players must strategically place a single explosion to destroy floating circles, triggering chain reactions that clear the entire screen. Each game is a 30-second challenge to maximize your score through clever positioning and timing.
+
+## Features
+
+- **One-Click Gameplay**: Simple to learn, challenging to master
+- **Chain Reaction Mechanics**: Destroyed circles trigger secondary explosions
+- **Dynamic Scoring**: Multiplier system rewards consecutive chain reactions
+- **Minimalist Design**: Beautiful pastel color palette with smooth animations
+- **Physics Simulation**: Realistic circle movement and collision detection
+- **Performance Optimized**: Handles 500+ circles at 60fps
+
+## Getting Started
+
+### Prerequisites
+
+- [Rust](https://rustup.rs/) (1.70.0 or later)
+- Cargo (comes with Rust)
+
+### Installation
+
+```bash
+# Clone the repository
+git clone https://github.com/yourusername/chain-reaction.git
+cd chain-reaction
+
+# Build and run
+cargo run --release
+```
+
+### Development Build
+
+```bash
+# Run in debug mode with faster compile times
+cargo run
+```
+
+## How to Play
+
+1. **Objective**: Clear all circles from the screen before time runs out (30 seconds)
+2. **Click** anywhere to create an explosion
+3. **Strategy**: Position your click to maximize the chain reaction
+4. **Scoring**:
+   - Base points for each destroyed circle
+   - Multiplier increases with consecutive chain reactions (1x → 2x → 4x → 8x...)
+   - Bonus points for clearing all circles in a single click
+
+### Controls
+
+- **Left Mouse Button**: Create explosion
+
+## Game Mechanics
+
+### Circles
+
+- Random sizes (10-50px radius)
+- Pastel color palette
+- Variable transparency (0.3-1.0)
+- Smooth physics-based movement
+
+### Explosions
+
+- Initial explosion radius: 100px
+- Chain reaction delay: 0.1s
+- Secondary explosions: 50% smaller radius
+- Cascading destruction creates satisfying combos
+
+## Technical Details
+
+**Built With:**
+
+- [Rust](https://www.rust-lang.org/) - Systems programming language
+- [Bevy](https://bevyengine.org/) - Data-driven game engine
+- Spatial partitioning for efficient collision detection
+
+## Roadmap
+
+See [GDD.md](GDD.md) for the complete game design document.
+
+### Potential Enhancements
+
+- [ ] Power-ups (larger explosions, time freeze)
+- [ ] Different circle types (fast/slow, bonus circles)
+- [ ] High score persistence
+- [ ] Multiple difficulty levels
+- [ ] Sound effects and music
+
+## Contributing
+
+Contributions are welcome! Feel free to:
+
+- Report bugs
+- Suggest new features
+- Submit pull requests
+
+## License
+
+See [LICENSE](LICENSE) for details.
+
+## Acknowledgments
+
+- Built with [Bevy Engine](https://bevyengine.org/)
+
+---
+
+**Enjoy creating explosive chain reactions!**