I'll create a single-page web app with a Gray-Scott reaction-diffusion simulation on canvas. The simulation will run in real-time with mouse interaction to seed new growth.

First, let me check the current directory and see if there's already an index.html file.

No files. I'll create index.html with a full simulation. I'll need to implement:

1. Canvas for display
2. Gray-Scott reaction-diffusion algorithm (two chemicals U and V)
3. Real-time simulation using WebGL or plain JavaScript (I'll use plain JS for simplicity)
4. Mouse interaction to add V (activator) at cursor position
5. Controls for parameters and patterns

I'll write the entire thing in one HTML file. Let's create it.

I'll create a single-page web app with a Gray-Scott reaction-diffusion simulation that grows organic Turing patterns in real time, with mouse interaction for seeding new growth.

I've created a complete Gray-Scott reaction-diffusion simulation web app in a single `index.html` file. Here's what it includes:

## Features:
- **Real-time simulation**: Runs a 512x512 Gray-Scott reaction-diffusion simulation
- **Mouse interaction**: Click and drag to seed new growth patterns
- **Parameter controls**: Adjust diffusion rates, feed/kill rates, brush size and intensity
- **Pattern presets**: Pre-configured parameters for different organic patterns (spots, worms, mazes, holes, chaos)
- **Controls**: Reset, pause/resume, and clear canvas buttons
- **Responsive design**: Works on both desktop and touch devices

## Technical Implementation:
- Uses HTML5 Canvas for rendering
- Implements the Gray-Scott equations with Laplace diffusion
- Real-time animation using requestAnimationFrame
- Color mapping based on chemical concentrations
- Gaussian brush for smooth interaction

## How to Use:
1. Open `index.html` in a web browser
2. Watch the organic patterns evolve automatically
3. Click and drag on the canvas to add substance B and trigger new patterns
4. Use the sliders to adjust simulation parameters
5. Try different pattern presets to see various organic formations

The simulation creates beautiful Turing patterns similar to those found in nature, like animal coats, seashell patterns, and biological morphogenesis. The file is completely self-contained with no external dependencies.