Add pending action abilities

[chubes4]

Summary

• Adds generic pending-action Abilities API entries for list, summary, get, and resolve.
• Adds host discovery filters for WP_Agent_Pending_Action_Store and WP_Agent_Pending_Action_Resolver without adding concrete storage.
• Adds pure-PHP smoke coverage and includes it in composer test.

Testing

• php -l src/Approvals/register-pending-action-abilities.php
• php -l tests/pending-action-abilities-smoke.php
• php -l tests/agents-api-smoke-helpers.php
• php tests/pending-action-abilities-smoke.php
• composer test
• homeboy lint --path /Users/chubes/Developer/agents-api@pending-action-abilities --extension wordpress --errors-only
• homeboy test --path /Users/chubes/Developer/agents-api@pending-action-abilities --extension wordpress

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Implemented the pending-action ability adapter, smoke coverage, simplify cleanup, and verification commands for Chris to review.