Add application configuration inspection commands

docs/config.md

@@ -95,6 +95,15 @@ The size fields must be zero or greater. The [HTTP API](api.md) defines how
 each limit is enforced and reported. `server.artifact_root` configures an HTTP
 deployment boundary; see [operations](operations.md) for deployment handling.
 
+The `config validate`, `config show`, and `config sources` commands inspect this
+application configuration without creating a Promptkit engine. `show` is a
+resolved inspection snapshot, not necessarily a reloadable file. Application
+validation does not check framework sources, backend connectivity, or credential
+availability. `api_key_env` is an environment-variable *name* and remains
+visible in inspection; its environment value is never read by ConfigKit.
+Ordinary backend `extra_params` values also remain visible, so keep secrets out
+of those fields and protect inspection output as potentially sensitive.
+
 ## Custom Backends
 
 Use `backends` when a profile selects an application-defined backend ID: