Switch CLI configuration to ConfigKit

docs/internal/adapters.md

@@ -18,6 +18,10 @@ described by its tagged
 - `internal/adapter/cli` resolves settings through `internal/config`,
   constructs `promptkit.Engine`, maps CLI values to `promptkit.RunRequest`,
   and owns output files, summaries, and exit codes.
+- `internal/config` delegates application YAML decoding, default resolution,
+  overrides, and validation ordering to ConfigKit. The CLI supplies only
+  explicitly visited application flags as overrides and renders safe structured
+  load diagnostics on stderr.
 - `internal/adapter/http` strictly decodes request DTOs, maps them to Promptkit
   public values, calls its adapter-owned `Runner` interface, and maps results
   and errors to HTTP DTOs.
@@ -53,7 +57,7 @@ not require prompt, schema, or artifact sources.
 with `promptkit.WithArtifactReader`, passes the engine through the HTTP
 adapter's consumer-owned `Runner` interface, and starts the server.
 
-All three CLI paths assemble the engine from the same resolved prompt, profile,
+The command paths assemble the engine from the same resolved prompt, profile,
 and schema directories plus configured custom backends. Each backend is mapped
 to Promptkit's public `Backend` value and registered during engine construction,
 so one constructed server engine retains one immutable backend registry and its