Add Ability Delegation Wrapper Infrastructure

[chubes4]

Summary

Add core infrastructure for the API plugin to act as a clean delegation wrapper to Abilities API. This transforms the API plugin from containing business logic to being a pure interface layer.

Current State

• API plugin contains 60+ REST routes with embedded business logic
• No Abilities API integration for delegation
• Direct function calls to other plugins throughout route handlers

Proposed Changes

• Add request/response transformation utilities between REST ↔ Abilities API
• Create helper functions for converting REST params to ability inputs
• Add error handling and response formatting for ability delegation
• Add ability discovery and validation utilities
• Maintain backward compatibility for existing REST endpoints

Technical Details

• New file: inc/core/ability-delegation.php with transformation utilities
• Helper functions: extrachill_api_rest_to_ability_input(), extrachill_api_ability_to_rest_response()
• Error mapping: Convert ability errors to appropriate HTTP status codes
• Input validation: Transform REST args to JSON schema validation

Success Criteria

• All existing REST endpoints continue to work unchanged
• Infrastructure ready to delegate to abilities as they become available
• Clean separation between interface (API) and implementation (plugin abilities)

Implementation Notes

• This is infrastructure only - no route conversions yet
• Test with mock abilities to ensure delegation pipeline works
• Document the delegation pattern for future route conversions