Migrate Renovate configuration to support GitHub Actions dependency management

[Copilot]

This PR migrates the Renovate configuration from the deprecated config:base preset to the modern config:recommended preset and adds explicit support for GitHub Actions dependency management.

Changes Made

• Updated renovate.json to use config:recommended instead of config:base
• Added explicit GitHub Actions support with "github-actions": {"enabled": true}
• Configured dependency grouping to bundle GitHub Actions updates together

Why These Changes Are Needed

The Dependency Dashboard issue identified that Renovate was detecting GitHub Actions dependencies in our workflows but the configuration migration was needed to properly manage them:

Detected Dependencies:

• actions/checkout@v5 (used in both workflows)
• ahmadnassri/action-dependabot-auto-merge@v2
• gitleaks/gitleaks-action@v2

Configuration Issues:

• The old config:base preset is deprecated
• GitHub Actions dependency management was not explicitly enabled
• No grouping configuration for cleaner dependency updates

Result

With this configuration, Renovate will now:

• Properly detect and manage GitHub Actions dependencies in .github/workflows/
• Create grouped PRs for GitHub Actions updates instead of individual PRs
• Work alongside the existing Dependabot configuration for gitsubmodules

The configuration maintains separation of concerns - Renovate handles GitHub Actions while Dependabot continues to handle gitsubmodules.

Fixes #946.

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