feat: per-agent MCP config and auto-detect transport

[napter]

Summary

This PR introduces two improvements to MCP (Model Context Protocol) handling:

1. Per-agent MCP configuration

Subordinate agents can now have their own dedicated MCP server configurations instead of sharing the global singleton. This enables hub-spoke architectures where different agent profiles connect to different MCP servers.

Changes:

• Added get_agent_mcp_config() function with per-config caching in mcp_handler.py
• Updated agent.py to use agent-aware MCP resolution
• Updated _10_system_prompt.py to use agent-aware MCP config for tool prompts
• Added get_profile_settings() in settings.py for loading per-profile settings overrides

2. MCP auto-detect transport

Remote MCP servers now default to auto transport type instead of sse. In auto mode, the client tries streamable HTTP first and falls back to SSE if that fails. This provides better compatibility with modern MCP servers.

Changes:

• Default transport type changed from sse to auto
• Added auto-detection logic with streamable HTTP → SSE fallback
• Added informative logging for transport selection