Add vaporwave squares sketch

[msfeldstein]

Adds a new canvas-sketch piece: vaporwave-squares.js

What it does:

• Draws 60 squares in classic vaporwave colors (hot pink, cyan, mint, purple, pale yellow, magenta, teal, etc.) on a deep purple gradient background
• Squares are a mix of filled and hollow, with varying sizes, opacities, and line widths
• Animated: each square drifts and rotates at its own speed, with gentle alpha pulsing
• Deterministic layout via a seeded PRNG so it looks the same on every load

Run it:

npx canvas-sketch vaporwave-squares.js --open