Revampt as dotnet-cat

Given https://www.linfo.org/cat.html definition:

cat is one of the most frequently used commands on Unix-like operating systems. It has three related functions with regard to text files: displaying them, combining copies of them and creating new ones.

And the catbag concept, we want to:

• Rename project to dotnet-cat
• Revamp implementation to use Spectre.Console for better progress and overall output
• Leverage proper globing for more precise sync
• Add significant test coverage to improve reliability since the globing isn't trivial

Some key features:

• Should allow flexible globing with multiple include/exclude strings, such as:

[file]
  url = https://github.com/git-ecosystem/git-credential-manager/tree/v2.6.0/src/shared/Core/Interop
  include = *.cs
  include = **/*FileSystem.cs
  exclude = **/MacOS/**/*.*

• CLI should allow specifying this via multiple -i|--include and -e|--exclude options.
• CLI should provide a --dry-run for all commands (including add, so you can test your include/excludes)
• Include/exclude would only be supported initially for github tree URLs (since it requires the GH CLI to fetch the directory contents)

Start by reviewing the existing CLI entry points, especially the add command, and the current handling of GitHub tree URLs; the issue names no files or tests. Done means the project is renamed, CLI output uses Spectre.Console, include/exclude globbing and dry-run options work as specified, and significant test coverage is added.