Create webcam contour-following particle swarm demo

[PGuuu]

Motivation

• Provide an interactive, browser-based particle swarm that visually tracks contours from a webcam feed so users can experiment with swarm behaviors and real-time contour-following effects.

Description

• Add a minimal UI page (index.html) with controls to start/stop the webcam and adjust particle count and a canvas to render the swarm.
• Add presentation styles in styles.css for a dark, canvas-centered layout and compact controls.
• Implement the swarm engine in script.js that extracts contour points from webcam frames using a luminance-gradient edge check, samples/limits points, and steers particles toward sampled contour points while rendering particles and soft connection lines.
• Manage webcam lifecycle, responsive canvas resizing, particle count adjustments via setParticleCount, and lightweight performance tuning (point sampling, capping, and update throttling).

Testing

• Ran node --check script.js to verify syntax and the check completed without errors.
• Served the demo locally with python3 -m http.server 4173 to validate the app loads and assets are served successfully.
• Captured a UI screenshot using a headless Playwright script to validate rendering and layout, and the screenshot artifact was produced successfully.

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Codex Task