Setup Dependabot for automated dependencies and security updates

[Aleks334]

Summary

Configure Dependabot to automate vulnerability scanning and version updates across the project. This will ensure our app remains secure and up-to-date while minimizing manual maintenance overhead.

https://docs.github.com/en/code-security/tutorials/secure-your-dependencies/dependabot-quickstart

Acceptance criteria

• dependabot.yml configuration file is added to the repository.
• Automated version updates are enabled for all environments: GitHub Actions, Docker, Client, and Server.
• Dependabot is configured to group updates into single PRs per package manager to reduce PR noise.
• Dependabot security alerts and automated security PRs are enabled in the repository settings.
• An update schedule (e.g. weekly, monthly) is defined in the configuration.

Notes

Verify that the automated PRs do not conflict with our current branch protection rules.