Allow subagents to use selected MCP tools

Hey Dmitri, I was checking whether Dirge subagents can use MCP tools configured for the main agent, and it seems they currently cannot.

My use case is a research subagent using codebase-memory-mcp to inspect the codebase, trace calls and look up relevant code.

Would it make sense to let agent profiles enable selected MCP servers or tools?

I may be missing an existing configuration option, so please let me know if this is already possible.

This is related to #700, but separate. The idea there is to add a persistent code graph to Dirge itself, while this would allow subagents to use an existing MCP server.