feat(channels/feishu): add domain config for Lark global support

Add 'domain' field to FeishuConfig (Literal['feishu', 'lark'], default 'feishu').
Pass domain to lark.Client.builder() and lark.ws.Client to support Lark global
(open.larksuite.com) in addition to Feishu China (open.feishu.cn).
Existing configs default to 'feishu' for backward compatibility.

Also add documentation for domain field in README.md and add tests for
domain config.

README.md

@@ -563,7 +563,8 @@ Uses **WebSocket** long connection — no public IP required.
       "reactEmoji": "OnIt",
       "doneEmoji": "DONE",
       "toolHintPrefix": "🔧",
-      "streaming": true
+      "streaming": true,
+      "domain": "feishu"
     }
   }
 }
@@ -576,6 +577,7 @@ Uses **WebSocket** long connection — no public IP required.
 > `reactEmoji`: Emoji for "processing" status (default: `OnIt`). See [available emojis](https://open.larkoffice.com/document/server-docs/im-v1/message-reaction/emojis-introduce).
 > `doneEmoji`: Optional emoji for "completed" status (e.g., `DONE`, `OK`, `HEART`). When set, bot adds this reaction after removing `reactEmoji`.
 > `toolHintPrefix`: Prefix for inline tool hints in streaming cards (default: `🔧`).
+> `domain`: `"feishu"` (default) for China (open.feishu.cn), `"lark"` for international Lark (open.larksuite.com).
 
 **3. Run**