Unify and Simplify CLI Command Architecture

[matrei]

Issue description

Handling of CLI commands is currently spread across multiple libraries, using different mechanisms for command registration.
This makes the architecture difficult to understand, maintain, and extend.
The goal is to align these approaches and introduce a clearer, more consistent command architecture.

Related: #15286

[jdaugherty]

Wouldn't it be better to focus on enhancing forge to replace profiles and consolidate into one cli?

[jamesfredley]

Having one approach to application and artifact generation in Grails 8 would be ideal, IE the consolidation of profiles and grails-forge-core.

For the other historical CLI uses cases, scripts/commands, intellij grails plugin integration, etc: I look forward to planning what that might look like. forge-cli is currently entirely offline, only focused on generation and does not use gradle or run the grails application, like shell-cli.