Feature Request: Add Deno to supported package managers

It would be great if UniGetUI could support Deno as a package manager alongside npm, bun, and others. Deno has its own package management and installation capabilities (like \deno install\), and integrating it would make managing Deno dependencies and global CLI tools much easier from the UI.

Start by examining how the existing npm and bun package managers are represented and integrated. Trace their package, installation, and global-tool flows, then determine how the capabilities named here—Deno dependency management and deno install—should appear in UniGetUI. Done means Deno is supported alongside the existing package managers for the requested UI workflows.

Written by the indexing model from the issue text.