Create make:model command

[ibourgeois]

Context

As a Laravel developer building packages in Nebula, I want to use php architect make:model to generate models with proper package namespacing and paths.

Acceptance Criteria

• Create MakeModelCommand class extending ArchitectCommand
• Support --package parameter to specify target package
• Override model path resolution to target package src/Models
• Override model namespace to use package namespace
• Ensure generated model inherits from Model correctly
• Add validation for package existence
• Add unit tests for model generation