supervisor-go: add ledger package with Append/Read APIs, tests; refactor CLI to use package; update README

kernel/supervisor-go/README.md

@@ -3,14 +3,30 @@
 Runnable stub demonstrating CognitiveOS control-plane concepts without
 an actual LLM.
 
-## Run
+This directory now contains a small ledger package (ledger/) with Append
+and Read APIs and unit tests, plus a tiny CLI demo (main.go) that
+appends route/session/output events to a JSONL ledger.
 
-go run . -ledger ./ledger.jsonl
+## Run (demo)
 
-Then type requests and observe: - deterministic route decision -
-session_spawn + child_output_received - final_output_emitted
+Build or run the CLI:
+
+    go run . -ledger ./ledger.jsonl
+
+Then type requests and observe the deterministic route decision,
+spawn/output events, and final output. The ledger file will be created
+as JSONL at the path you provide.
+
+## Tests
+
+Run the unit tests for the ledger package:
+
+    go test ./ledger
+
+The tests create a temporary ledger file, append events, and validate
+read-back and hash chaining.
 
 ## Notes
 
--   This is intentionally minimal and deterministic.
--   Replace `childWorkerStub` with real model calls later.
+- This is intentionally minimal and deterministic.
+- Replace `childWorkerStub` with real model calls later.