🤖 Experiment: Add filtering capabilities to WordPress Abilities API

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This PR implements comprehensive filtering functionality for the WordPress Abilities API to address the challenge of managing large numbers of registered abilities from core and plugins.

What's New

Core Filtering System

• New WP_Abilities_Query class: Provides a WordPress-style query interface for filtering abilities
• Enhanced wp_get_abilities() function: Now accepts optional query parameters while maintaining full backward compatibility
• REST API filtering: All filtering options are available via REST API query parameters

Filtering Options Available

Namespace filtering: Filter abilities by plugin/namespace prefix

$abilities = wp_get_abilities( array( 'namespace' => 'my-plugin' ) );

Text search: Search abilities by label or description (case-insensitive)

$abilities = wp_get_abilities( array( 'search' => 'math' ) );

Schema presence filtering: Filter by input/output schema availability

$abilities = wp_get_abilities( array( 'has_input_schema' => true ) );

Meta query filtering: WordPress-style meta queries with multiple operators

$abilities = wp_get_abilities( array(
    'meta_query' => array(
        array(
            'key'   => 'category',
            'value' => 'ai',
        ),
    ),
) );

Combined filtering: All filters can be used together

$abilities = wp_get_abilities( array(
    'namespace'        => 'my-plugin',
    'search'           => 'process',
    'has_input_schema' => true,
) );

REST API Integration

The REST API now supports all filtering options via query parameters:

GET /wp-json/wp/v2/abilities?namespace=my-plugin&search=math&has_input_schema=true

Backward Compatibility

The changes are fully backward compatible:

• wp_get_abilities() without parameters continues to return all abilities
• Existing REST API endpoints work unchanged
• No breaking changes to existing functionality

Implementation Details

• Performance-conscious: Filtering is done in-memory after loading abilities
• Type-safe: Full PHPDoc annotations and strict typing
• Standards-compliant: Passes WordPress coding standards
• Well-tested: Comprehensive test coverage included
• Documented: Complete documentation with examples

This implementation follows WordPress conventions (similar to WP_Query, WP_User_Query) and provides the scalability needed for managing abilities in environments with many registered items.

Fixes #38.

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