Add Filament Actions documentation to AI context

[leandrocfe]

Please review this PR in Laravel Roster before proceeding, as it contains related changes.

Summary

Filament is composed of several packages, as detailed in the Filament Documentation.

This PR adds comprehensive Filament Actions documentation to .ai/filament-actions/ to provide AI context about:

• Core concepts: Action workflows, triggers, modals, and execution logic
• Key features: Action types/styles, prebuilt actions, authorization, confirmations, modal forms, wizards, and custom content
• Livewire integration: Using actions in custom components, passing arguments, grouping, and programmatic triggering
• Testing: Action testing utilities with Pest
• Version-specific documentation: Separate guides for v3 and v4 with their respective features and differences

This documentation helps AI assistants better understand Filament Actions usage patterns, best practices, and available features when working with the codebase.

If you approve this PR, I will proceed to add documentation for other Filament packages in subsequent PRs.