chore: configure Dependabot schedule and grouping

[mostronatorcoder]

Description

Optimize the Dependabot configuration for better dependency management.

Current state

Dependabot is active but creates individual PRs for each dependency bump, which can be noisy and hard to manage.

Proposal

1. Group minor/patch updates into a single weekly PR to reduce noise
2. Keep major updates as individual PRs for careful review
3. Set a weekly schedule (e.g., Monday) instead of daily
4. Add GitHub Actions ecosystem to also keep CI dependencies updated

Example .github/dependabot.yml:

version: 2
updates:
  - package-ecosystem: npm
    directory: /
    schedule:
      interval: weekly
      day: monday
    groups:
      minor-and-patch:
        update-types:
          - minor
          - patch
    open-pull-requests-limit: 10

  - package-ecosystem: github-actions
    directory: /
    schedule:
      interval: weekly
      day: monday

Benefits

• Fewer PRs to review (grouped minor/patch)
• Predictable schedule (weekly on Mondays)
• CI actions also stay updated
• Major bumps still get individual attention