build: implement automated GitHub Releases and CI validation

[yaroher]

Summary
This PR establishes a complete CI/CD pipeline for the JetBrains plugin, enabling automated testing, artifact generation, and official GitHub Releases.

Key Changes

• Automated GitHub Releases (.github/workflows/release.yml):
• Trigger: Automatically runs on pushes to the release branch or when a version tag (v*) is created.
• Release Creation: Automatically creates an official GitHub Release using the version defined in build.gradle.kts.
• Asset Attachment: Builds and attaches the signed plugin .zip distribution directly to the GitHub Release.
• Marketplace Integration: Ready for JetBrains Marketplace publishing (activated by adding the PUBLISH_TOKEN secret).
• Robust CI Workflow (.github/workflows/ci.yml):
  • Ensures every PR and push to main/dev is validated via ktlint, full build, and unit tests.
  • Uploads a build artifact for every run, allowing developers to test the plugin ZIP without creating a formal release.
• Gradle Configuration Cleanup:
  • Removed obsolete kotlin.yml workflow.
  • Cleaned up settings.gradle.kts by removing non-existent modules.
  • Optimized for Java 17/21 (required for IntelliJ Platform 2025.1+).