chore(deps): SHA-pin github workflows and introduce dependabot

[frenchi]

Introduces Dependabot & SHA-pins workflow deps, as per the Discord thread. Thanks @PederHP for your input.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• CI & Patching housekeeping

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed