Clean up unused Zemeroth demo artifacts

[YfengJ]

Closes #28.

Summary

• rename the live canvas demo from demo/zemeroth-demo to demo/human-vs-bots
• remove the unused Zemeroth engine artifacts (zemeroth.wasm, gl.js) and the unreferenced RON/font payload left with that demo folder
• remove Zemeroth-only third-party license files now that those artifacts are gone
• update the root redirect, README route/script references, and replace serve-zemeroth.sh with serve-human-vs-bots.sh

Validation

• bash -n scripts/serve-human-vs-bots.sh scripts/serve-demos.sh scripts/game-studio.sh
• test -f demo/human-vs-bots/index.html
• test ! -e demo/zemeroth-demo
• test ! -e THIRD_PARTY_ZEMEROTH_LICENSE_MIT.txt
• test ! -e THIRD_PARTY_ZEMEROTH_LICENSE_APACHE.txt
• ! rg -n "zemeroth|Zemeroth|serve-zemeroth" README.md index.html scripts demo -S
• git diff --cached --check
• served the repo with python3 -m http.server and confirmed /, /demo/human-vs-bots/, game.js, and styles.css all resolve
• ran ./scripts/serve-human-vs-bots.sh and confirmed the direct demo page serves with game.js

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.7% Duplication on New Code

See analysis details on SonarQube Cloud