Add Dependabot or Renovate for automated dependency updates

[jose-compu]

Description

Dependencies should be kept up to date to receive security patches and bug fixes. Automated dependency update tools create PRs when new versions are available.

Proposed Changes

• Add .github/dependabot.yml with:
  • cargo package ecosystem updates (weekly)
  • github-actions ecosystem updates (weekly)
• Alternatively, configure Renovate with a renovate.json

Impact

Automated security patches and dependency freshness.