This PR introduces a new REST endpoint for discovering and listing ability categories.

Why

Following PRs #102 and #114 which introduced the categories system, we need a way to expose category information via the REST API so that it can be used in places like the command pallete, agents, etc.

External systems and AI agents need to discover what categories exist before they can effectively filter and query abilities.

Additionally, the existing abilities endpoints were accessible to any authenticated user with read capability, which could return meta information about available capabilities to subscribers (though, I believe they would need an application password setup). I've updated the permission check to require manage_options instead, which I think might be better for the endpoints. What do you think?

How

Created a new WP_REST_Abilities_Categories_Controller:

• New endpoints - GET /wp/v2/abilities/categories (list) and GET /wp/v2/abilities/categories/{slug}
• _links - Each category response includes self, collection, and abilities links for API discoverability
• Pagination - Supports pagination with page/per_page parameters (default 50, max 100)
• Admin-only access - Changed permission check from read to manage_options for both categories and abilities endpoints (see note above)
• Test cases - Test cases covering list operations, permissions, pagination, links, and edge cases

How to Test

Make sure that you have a few categories and Abilities registered.

npm run test:php
npm run lint:php

1. List categories

   curl -u "admin:APP_PASSWORD" \
     https://example.com/wp-json/wp/v2/abilities/categories

   • Should return array of categories with pagination headers
   • Each category should include pagination links to self, collection, and abilities

2. Get single category

   curl -u "admin:APP_PASSWORD" \
     https://example.com/wp-json/wp/v2/abilities/categories/data-retrieval

   • Should return category details with slug, label, description, meta

3. Test pagination

   curl -u "admin:APP_PASSWORD" "https://example.com/wp-json/wp/v2/abilities/categories?per_page=2"

   • Check X-WP-Total and X-WP-TotalPages headers

4. Test filtering abilities by category

   curl -u "admin:APP_PASSWORD" \
     "https://example.com/wp-json/wp/v2/abilities?category=data-retrieval"

   • Should return only abilities in the specified category

5. Test permissions

   # Without authentication (should fail with 401)
   curl https://example.com/wp-json/wp/v2/abilities/categories
   
   # With non-admin user (should fail with 403)
   curl -u "subscriber:APP_PASSWORD" \
     https://example.com/wp-json/wp/v2/abilities/categories

6. Test 404 handling

   curl -u "admin:APP_PASSWORD" \
     https://example.com/wp-json/wp/v2/abilities/categories/non-existent

   • Should return 404 with rest_category_not_found error code