The official MCP configuration schema uses `transport` to specify the
transport mechanism (stdio/sse/http), but `McpServerConfig` only honored
`type` and defaulted to `stdio`. Remote MCP servers configured with just
`transport: sse` were therefore misidentified as stdio and failed with
"with stdio transport requires 'command' field".
Add a model validator that promotes `transport` to `type` when only
`transport` is provided, while keeping `type` authoritative when both
are set. This matches the MCP-spec field name without breaking existing
configurations.
Fixes#3238
8fca56cf43