#7 ci(web): publish WASM demo to GitHub Pages from main

Publishes the existing verified WASM demo artifact on relevant pushes to main instead of leaving deployment manual-only.

Changes:

• keep the existing build/output verification
• deploy only from refs/heads/main
• keep manual redeploy support on main
• serialize Pages deployments without cancelling an in-flight production deploy

This should turn the currently skipped Pages deploy into an actual deployment after merge.

Summary by Sourcery

Publish the verified WebAssembly demo to GitHub Pages automatically from main while preserving safe, manual redeployments.

New Features:

• Publish the verified WebAssembly demo to GitHub Pages on pushes to the main branch while retaining manual redeployment support.

Enhancements:

• Serialize Pages deployments without cancelling in-progress production deployments.

CI:

• Update the Pages workflow to deploy only from refs/heads/main after successful build and output verification.

Deployment:

• Enable automatic GitHub Pages deployment for relevant main-branch updates.

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Summary by cubic

Publishes the WASM demo to GitHub Pages on every push to main, replacing the previous manual-only deployment. The existing build verification stays, manual redeploy from main is still possible, and Pages deployments now serialize without cancelling an in-flight production deploy.