chore: add Dependabot configuration for automated dependency updates

[dbebawy]

Summary

Adds Dependabot configuration to automatically keep pub dependencies up-to-date.

Configuration

version: 2
updates:
  - package-ecosystem: "pub"
    directory: "/"
    schedule:
      interval: "weekly"
    open-pull-requests-limit: 10
    labels:
      - "dependencies"

Benefits

• Automated PRs: Dependabot will create PRs for dependency updates weekly
• Security alerts: Get notified of security vulnerabilities in dependencies
• Reduced maintenance: Less manual work tracking outdated dependencies
• Ecosystem compatibility: Keeps the package compatible with the broader Dart/Flutter ecosystem

Why this matters

Issues like #319, #285 (outdated get_it constraint) could be avoided with automated dependency updates. Dependabot would have created a PR when get_it 9.x was released.

Related

• Fixes [FEATURE REQUEST] Enable Dependabot for automated dependency updates #321