Add canonical chat run lifecycle events

[chubes4]

Summary

• Add the unopinionated agents/list-chat-run-events ability contract for client-addressable chat run lifecycle events.
• Route event reads through a host/runtime-provided wp_agent_chat_run_events_handler; Agents API core does not persist lifecycle events or add new storage.
• Preserve existing run-control behavior while normalizing handler output for run_id, session_id, status, events, cursor, and has_more.

Refs #244.

Testing

• php -l src/Runtime/class-wp-agent-chat-run-control.php
• php -l src/Runtime/class-wp-agent-conversation-loop.php
• php -l src/Channels/register-agents-chat-run-control-abilities.php
• php -l tests/chat-run-control-smoke.php
• php -l tests/conversation-loop-events-smoke.php
• php tests/chat-run-control-smoke.php
• php tests/conversation-loop-events-smoke.php
• homeboy lint --changed-since origin/main
• composer test

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafting the implementation, smoke coverage, and PR description; Chris remains responsible for review and testing.