Global shide directory, ~/.config/shide

Allows specifying commands that can be used in any project; has its own node_modules, and shide version.

Name conflicts between local and global? Maybe command 'foo' would be `shide-user:foo` or `shide-global:foo` instead of `shide-command:foo`.

The issue does not name any files, tests, or entry points. First clarify the design for a global ~/.config/shide directory, its node_modules and shide version, and how local/global command name conflicts should work. Done should include an agreed scope and behavior for these cases.

Written by the indexing model from the issue text.