Feat: Hash routing for math demo deep links

[arossti]

Summary

• Add URL hash routing so math demos can be opened directly via deep links
• Supports 7 demos: #quadrance, #cross, #weierstrass, #gravity, #color, #rotors, #prime
• Auto-opens the corresponding demo modal on page load
• Listens for hashchange events for subsequent navigation

How it works

The hash fragment maps to existing demo link element IDs. On page load (and hashchange),
the handler simulates a click on the corresponding link, which triggers the existing
lazy-init + modal-open logic.

Use cases

• External links: https://arossti.github.io/ARTexplorer/#quadrance
• Native macOS app Help menu → opens browser at specific demo
• Shareable demo links for educational contexts

Test plan

• Visit https://arossti.github.io/ARTexplorer/#quadrance — Quadrance demo opens
• Visit #cross, #weierstrass, #gravity — corresponding modals open
• Visit #color, #rotors, #prime — non-modal demos activate
• Visit without hash — no demo auto-opens (normal behavior)
• Change hash in URL bar — demo switches

🤖 Generated with Claude Code

[github-actions]

🤖 Claude Code Review

API Error: x-api-key header is required

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