Implements issue #274 - migrates development tasks from Just to Mask task runner.

Changes Made

🔄 Migration Overview

• Replaced justfile with maskfile.md
• Updated CONTRIBUTING.md to reference Mask instead of Just
• Maintained all existing functionality with identical command behavior

📋 Available Tasks

All original Just tasks have been migrated to Mask with the same functionality:

🎯 Why Mask?

As mentioned in the issue, Mask provides the advantage of being "Markdown everything" - the maskfile.md serves as both human-readable documentation and executable task definitions. This aligns perfectly with Marmite's documentation-focused approach.

🧪 Testing

• ✅ All existing tests pass
• ✅ All Mask commands work identically to original Just tasks
• ✅ Code formatting and linting complete successfully
• ✅ Build process remains unchanged

📖 Documentation Updates

Updated CONTRIBUTING.md to guide contributors to use Mask instead of Just:

# Before
cargo install just
just check

# After  
cargo install mask
mask check

🔧 Installation

Contributors can install Mask via:

cargo install mask

The maskfile.md will be automatically discovered and parsed by Mask when running commands in the project root.

Closes #274

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.