Enable user-defined appstore sources - #299

Cannot invoke "ksp.com.intellij.openapi.application.Application.getService(java.lang.Class)" because the return value of "ksp.com.intellij.openapi.application.ApplicationManager.getApplication()" is null

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, actions/setup-java@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/