feat: add /ego-mgr slash command

Add /ego-mgr slash command with subcommands:
- get, set, list, delete, add-column, add-public-column, show
- Uses pcexec to call ego-mgr binary with proper env vars

Translate all Chinese text to English in responses.

Note: pcexec tool name and function names remain unchanged.

plugin/openclaw.plugin.json

@@ -2,7 +2,7 @@
   "id": "padded-cell",
   "name": "PaddedCell",
   "version": "0.2.0",
-  "description": "Secure password management, safe execution, and coordinated agent restart",
+  "description": "Secure secret management, agent identity management, safe execution, and coordinated agent restart",
   "entry": "./index.js",
   "configSchema": {
     "type": "object",