docs: add issue templates, pull request template, and update issue links - #237

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: hendrikmuhs/ccache-action@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Gradle 8.13 is out of date: consider updating to the latest Gradle version. See https://docs.gradle.org/current/userguide/feature_lifecycle.html#eol_support