fix: preserve interactive CLI formatting for async subagent output

[ducheng121]

Fixes #1904

Summary

Fix interactive CLI output corruption when async subagent completion messages arrive while the user is typing.

Cause

The CLI used prompt_toolkit for interactive input, but async outbound messages were rendered by Rich directly to the terminal. This could corrupt the prompt and leak ANSI control sequences like ?[36m...?[0m.

Fix

• Keep Rich/Markdown rendering for async replies
• Render async output to ANSI first
• Send that ANSI through prompt_toolkit safe terminal output instead of writing directly to stdout

Verification

Manually tested:

• async subagent completion while typing
• async reply with Markdown formatting
• interactive CLI prompt remains intact

[chengyongru]

Hi @ducheng121

Thanks for your working!