We need respond by creating index.html in cwd. Need build single-page web app self-contained no external resources. Need inspect cwd maybe empty. Need implement Gray-Scott reaction-diffusion simulation canvas real time organic Turing patterns mouse seeding. Need probably use HTML CSS JS all inline. Need final concise. Need create file. Need maybe use write. Need ensure robust. Let's plan implementation.

Need produce index.html. Requirements:
- Canvas grows organic Turing patterns in real time.
- Mouse seeding new growth.
- No external resources/network.
- Single file.

Implement Gray-Scott reaction-diffusion:
Grid dimensions maybe 240x160 internal, render scaled to canvas. Arrays feed and inhibit floats, next arrays. Initialize feed=1, kill=0.054, D_a=1, D_b=0.5. Seed initial spots with B high and F reduced maybe. At each step compute laplacian with convolution for A=1-B. A=1-B, B=B. update:
A = A + (Da*lapA - A*B*B + feed*(1-A))*dt
B = B + (Db*lapB + A*B*B - (kill+feed)*B)*dt
Clamp. Use dt maybe 1.0.
Need color based on B or laplacian maybe organic. Canvas CSS full viewport. UI controls maybe sliders for feed, kill, rate, palette, seed. Use pointer events to seed new growth. Mouse seeding new growth: on pointerdown/move while down, add circular B spots with F maybe. Also maybe auto seed if no mouse. Need avoid external.

Need high performance. JS typed arrays Float32Array. Grid width/height maybe based on canvas internal size; if canvas CSS full window, internal resolution maybe 280x180 for performance. Render each frame by ImageData at internal res then scale. But if canvas width/height equal internal maybe pixelated. Could use CSS image-rendering? Organic smoother maybe use low res and draw scaled. For real time, compute at 220x140. Could dynamically set simulation dimensions based on viewport: maybe 260x165. We can have internal canvas for imageData and visible canvas. But one <canvas> can use low res and CSS scale. Need handle device pixel ratio? For performance, set canvas.width = simW, height = simH, style width=100vw. But canvas width attribute low; CSS full. Good.

Need render: For each cell, b = B[i], maybe color. In Gray-Scott, A=1-B. Visualize B high dark/blue, low background. Organic Turing patterns.