Multi-domain routing

Tag a tool with multiple domains to make it available in each:

POST /mcp/operator    -> tools tagged "operator"
POST /mcp/recruiting  -> tools tagged "recruiting"
POST /mcp             -> tools tagged with default_domain

Tag a tool with multiple domains to make it available in each:

tags "operator", "recruiting"

Collected from README.md in the repository. Edit it there, not here.