Add model-aware Filterable::for() factory

[kettasoft]

Summary

Add a convenient Filterable::for() factory for creating fully initialized filter instances from Eloquent models or existing query builders.

Changes

• Support model class names, model instances, and Eloquent builders.
• Initialize and expose the builder immediately.
• Preserve existing builder constraints.
• Derive the model automatically from supplied builders.
• Support custom requests, facades, and late static binding.
• Improve fluent builder forwarding for Filterable and Invoker.
• Document the new factory API.