Add standalone Mandelbrot set renderer in JavaScript

[Copilot]

Summary

Adds a small, dependency-free Mandelbrot set renderer using plain JavaScript and the HTML5 Canvas API.

What it does

• Renders the Mandelbrot set with smooth (continuous) coloring
• Interactive zoom via scroll wheel or click (shift+click to zoom out)
• Drag-to-pan navigation
• Iteration budget auto-increases when zooming in for finer detail
• Cardioid / period-2 bulb early-out checks for faster rendering of interior regions
• "Reset View" and "Save PNG" buttons

Usage

Open examples/mandelbrot/index.html directly in a browser - no build step needed.

Testing

• Verified core escape-time math logic in isolation (in-set points reach max iterations, out-of-set points escape quickly, boundary points behave as expected)
• Syntax-checked the extracted JS with node --check
• Could not run a full headless-browser visual screenshot in this sandbox (Playwright browser download stalled on network), but the algorithm and interaction logic were verified directly.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com