Desktop Extensions according to modelcontextprotocol manifest

[SebbeJohansson]

This pull request adds support for building and distributing a Claude Desktop extension (.mcpb package) for Contractbook. It introduces a new build script, manifest, and packaging process, updates CI/CD workflows to automate building and releasing the extension, and improves documentation for users and admins.

Sources: https://github.com/modelcontextprotocol/mcpb

Build and packaging for Claude Desktop:

• Added scripts/pack-mcpb.mjs to automate packaging the extension, including production dependencies and manifest, into build/contractbook.mcpb using the MCPB CLI.
• Added mcpb/manifest.json describing the extension for Claude Desktop, including metadata, server entry point, user configuration, and compatibility.
• Introduced a new build:mcpb script in package.json to run the build and packaging process.

CI/CD workflow enhancements:

• Updated .github/workflows/ci.yml and .github/workflows/publish.yml to run the new build:mcpb script as part of CI and release publishing, ensuring the .mcpb file is built and included in releases. [1] [2]
• Automated creation of a GitHub release asset for the .mcpb file, attaching it to each release.

Documentation improvements:

• Expanded README.md with installation instructions for Claude Desktop users and admins, and detailed the build and packaging process for the extension.

[SebbeJohansson]

No idea if you are interested in having a mcpb implementation, but I made one for RevolutionRace so thought i might aswell make a PR.