feat: procedural terrain generators with example script and bilingual tutorial docs - #53

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11d5960a326750d5838078e36cf38b85af677262, github/codeql-action/analyze@6f5948dfacef28e207b48d0905cf90c03365536d, github/codeql-action/init@6f5948dfacef28e207b48d0905cf90c03365536d. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/