Schema for creating an MCP server config.

Creating an MCP server config also:

1. Validates the URL (SSRF checks)
2. Tests the connection by calling tools/list on the remote server
3. Creates an auth_config for the credentials (or uses an existing one)

If the connection test fails, no records are created.

Provide either auth_config (inline creation) or auth_config_id (pre-existing),
but not both. Use auth_config_id when the auth config was created separately,
e.g. after completing an OAuth authorization flow via the /auth_configs and /oauth endpoints.