feat(cli): add portable data backup and restore

docs/zh/cli/index.mdx

@@ -44,6 +44,10 @@ Memory & Knowledge:
   memory    Memory distillation (dream)
   knowledge View knowledge base stats and structure
 
+Data portability:
+  backup    Back up config and agent workspace
+  restore   Restore a CowAgent backup
+
 Others:
   help      Show this help message
   version   Show version
@@ -92,6 +96,7 @@ Others:
 | start / stop / restart | ✓ | ✗ |
 | update | ✓ | ✗ |
 | install-browser | ✓ | ✗ |
+| backup / restore | ✓ | ✗ |
 
 <Note>
   `context` 在终端中仅提示到对话中使用。`config` 仅支持在对话中修改。