Fix Mermaid graph label quoting in README files

Updated the Mermaid diagrams in all README variants to quote the Wait (Backoff) node label, ensuring correct rendering of labels with parentheses.

README.zh-Hant.md

@@ -166,7 +166,7 @@ graph TD
     Upstream -->|成功| ProcessResponse[處理回應]
     Upstream -->|失敗| Retry{重試?}
     
-    Retry -->|是| Wait[等待 (退避)] --> Upstream
+    Retry -->|是| Wait["等待 (退避)"] --> Upstream
     Retry -->|否| Error
     
     ProcessResponse --> Finalize[添加標頭並返回]