Add pack diff command

docs/agent-setup.md

@@ -60,6 +60,7 @@ python scripts/mcp_smoke_test.py
 
 - `pack_keygen`
 - `pack_build`
+- `pack_diff`
 - `pack_list`
 - `pack_verify`
 - `pack_extract`

docs/mcp.md

@@ -44,6 +44,13 @@ Inputs:
 - `key_file`
 - `signing_secret_key_file`
 
+### `pack_diff`
+
+Inputs:
+
+- `left`
+- `right`
+
 ### `pack_list`
 
 Inputs: