List MCP servers connected to the org (resolver helper)

Return MCP servers (with their tool lists) for tool.mcp_server_id resolution.

org_id is REQUIRED by voice (voice/graph8_livekit/routers/mcp_servers.py declares list_mcp_servers(org_id: str) with no default), so omitting it makes voice answer 422, not an empty list. This route previously sat below the /{action_id} catch-all and was unreachable, which hid the missing parameter - un-shadowing it turned a 404 into a 422 until this was fixed.

The org is pinned from the authenticated caller and is never read from the request, so a client cannot enumerate another tenant's MCP servers.