Add JSON-RPC task method compatibility

[chubes4]

Summary

• Accept legacy Agent Protocol task method names as aliases for the JSON-RPC chat adapter: tasks/send and tasks/sendSubscribe.
• Preserve top-level tokenStreaming from JSON-RPC requests in the canonical chat input.
• Extract clientContext from Agent Protocol data message parts into canonical chat client context.
• Extend pure-PHP smoke coverage for aliases, data-part context, token streaming, and sync dispatch.

Verification

• composer test
• homeboy deps install agents-api
• homeboy lint agents-api

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Implementing the generic JSON-RPC compatibility patch, adding smoke coverage, and running verification.