Fix runtime package ability late registration

[chubes4]

Summary

• preserve the normal wp_abilities_api_init registration path for runtime package abilities
• register the runtime package ability/category through the backing Abilities registries when Agents API loads after the one-shot Abilities API hooks have already fired
• add smoke coverage that resolves agents/run-runtime-package through wp_get_ability() in a late/headless lifecycle and executes it through the canonical ability object with a handler filter

Testing

• php -l src/Runtime/register-runtime-package-run-ability.php
• php -l tests/runtime-package-run-contract-smoke.php
• php tests/runtime-package-run-contract-smoke.php
• composer smoke

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Agents API ability lifecycle investigation, implementation, and test drafting.