Support shorthand aliases for plugin commands

Feature Request

Allow plugins to define shorthand aliases for their commands, so users don't always have to type the fully qualified /<plugin-name>:<command-name> form.

Current Behavior

All plugin commands require the fully qualified namespace:

/ralph-loop:ralph-loop
/commit-commands:commit
/ralph-loop:cancel-ralph

This is verbose and slows down workflow, especially for frequently used commands.

Proposed Behavior

Allow plugins to define short aliases in their plugin.json (or a similar config), so users can type:

/ralph        → /ralph-loop:ralph-loop
/commit       → /commit-commands:commit
/cancel-ralph → /ralph-loop:cancel-ralph

For example, a plugin could declare aliases like:

{
  "commands": {
    "ralph-loop": { "alias": "ralph" },
    "cancel-ralph": { "alias": "cancel-ralph" }
  }
}

If two plugins register the same alias, the fully qualified form would still be required to disambiguate.

Motivation

Plugin commands are frequently invoked interactively. The plugin:command namespace is important for avoiding collisions, but users should have the option of shorter invocations for common workflows. This is especially painful when the plugin name and command name are identical (e.g., /ralph-loop:ralph-loop).