Initialize JetBrains Junie 🚀

[jetbrains-junie]

This PR initializes JetBrains Junie 🚀 by adding essential configuration files.

Includes:

• GitHub workflow for automated execution
• Dev container setup (if applicable)
• Language-specific scripts (if applicable)

Generated automatically by Junie. Review and customize as needed.

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Summary by cubic

Sets up JetBrains Junie with a GitHub Actions workflow and a Java dev container. Enables manual Junie runs and a consistent local environment with Maven and Gradle.

• New Features
  • GitHub Actions: Junie workflow (manual trigger) sends run_id and workflow_params to jetbrains-junie/junie-workflows/ej-issue.yml with contents: write permission.
  • Dev container: Java 21 base image with Maven 3.8.6 and Gradle installed.

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