fix(chat): resolve run_in_chat_io_executor keyword argument mismatch (#2958)

[mrveiss]

Summary

• run_in_chat_io_executor() wraps loop.run_in_executor() which doesn't forward kwargs
• Updated executor to accept **kwargs and bind them via functools.partial before dispatch
• Fixes chat session listing and saving failures caused by exist_ok=True kwarg

Closes #2958

Test plan

• Verify chat session listing works without unexpected keyword argument errors
• Verify chat session saving works
• Check backend logs for any remaining executor errors

🤖 Generated with Claude Code

[github-actions]

⚠️ SSOT Configuration Compliance: Violations Found

Metric	Count
Total Violations	3
SSOT Violations (high priority)	2
Other Violations	1

⚠️ 2 values have SSOT config equivalents!

These should be replaced with SSOT config imports:

Python:

from src.config.ssot_config import config
# Use: config.vm.main, config.port.backend, config.backend_url

TypeScript:

import config from '@/config/ssot-config'
// Use: config.vm.main, config.port.backend, config.backendUrl

📖 See SSOT_CONFIG_GUIDE.md for documentation.