Add Dependabot configuration for Composer, npm, and GitHub Actions

[Copilot]

This adds a standard Dependabot v2 configuration for the dependency ecosystems already used in the repository, with all update PRs targeting master. The config covers Composer, npm, and GitHub Actions on a weekly schedule.

• Dependabot configuration

  • Add .github/dependabot.yml
  • Set version: 2
  • Configure updates for:
    • composer in /
    • npm in /
    • github-actions in /

• PR targeting

  • Set target-branch: master for each ecosystem so automated dependency update PRs are opened against the repository’s base branch

• Schedule

  • Use a conventional weekly cadence for all update entries

version: 2
updates:
  - package-ecosystem: composer
    directory: /
    schedule:
      interval: weekly
    target-branch: master

  - package-ecosystem: npm
    directory: /
    schedule:
      interval: weekly
    target-branch: master

  - package-ecosystem: github-actions
    directory: /
    schedule:
      interval: weekly
    target-branch: master