feat(abilities): add related posts ability

[rbcorrales]

Summary

1. Registers wpvdb/find-related-posts as a read only MCP public Ability.
2. Wraps Search::related_to_post() and returns agent safe related post results with canonical URLs.
3. Documents the Ability and MCP usage, refreshes translations, and adds unit coverage.

Test steps

1. Deploy wpvdb-search to a test site with MCP Adapter active.
2. Initialize the MCP endpoint and call mcp-adapter-discover-abilities. Confirm wpvdb/semantic-search and wpvdb/find-related-posts appear.
3. Call mcp-adapter-execute-ability with ability_name set to wpvdb/find-related-posts and a source post_id. Confirm the response has mode set to related and returns related results.

[Copilot]

Pull request overview

Adds a second public Abilities/MCP tool wpvdb/find-related-posts that wraps Search::related_to_post(), returning the same agent-safe result projection as the existing semantic search ability. Includes input/output schemas, README + POT/PO updates, and new unit coverage along with bootstrap stubs needed to exercise the abilities layer.

Changes:

• Register wpvdb/find-related-posts ability with input/output schemas and reuse format_results() for agent-safe output.
• Expand README and translation catalogs to document the new ability.
• Add AbilitiesTest plus Abilities/API/user/transient stubs in the test bootstrap.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
includes/class-abilities.php	Adds FIND_RELATED constant, registration, executor, and input/output schemas for related-post lookup.
README.md	Documents the new ability and its REST route alongside semantic search.
languages/wpvdb-search.pot	New translatable strings for the related ability.
languages/wpvdb-search-es_ES.po	Spanish translations (several marked fuzzy) for the related ability strings.
tests/Unit/AbilitiesTest.php	New tests covering ability registration and related execution paths.
tests/bootstrap.php	Adds stubs (add_action, caps, transients, wp_register_ability*, get_post_type_object) and loads the abilities class.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.