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.

tests/channels/test_feishu_domain.py

@@ -0,0 +1,48 @@
+"""Tests for Feishu/Lark domain configuration."""
+from unittest.mock import MagicMock
+
+import pytest
+
+from nanobot.bus.queue import MessageBus
+from nanobot.channels.feishu import FeishuChannel, FeishuConfig
+
+
+def _make_channel(domain: str = "feishu") -> FeishuChannel:
+    config = FeishuConfig(
+        enabled=True,
+        app_id="cli_test",
+        app_secret="secret",
+        allow_from=["*"],
+        domain=domain,
+    )
+    ch = FeishuChannel(config, MessageBus())
+    ch._client = MagicMock()
+    ch._loop = None
+    return ch
+
+
+class TestFeishuConfigDomain:
+    def test_domain_default_is_feishu(self):
+        config = FeishuConfig()
+        assert config.domain == "feishu"
+
+    def test_domain_accepts_lark(self):
+        config = FeishuConfig(domain="lark")
+        assert config.domain == "lark"
+
+    def test_domain_accepts_feishu(self):
+        config = FeishuConfig(domain="feishu")
+        assert config.domain == "feishu"
+
+    def test_default_config_includes_domain(self):
+        default_cfg = FeishuChannel.default_config()
+        assert "domain" in default_cfg
+        assert default_cfg["domain"] == "feishu"
+
+    def test_channel_persists_domain_from_config(self):
+        ch = _make_channel(domain="lark")
+        assert ch.config.domain == "lark"
+
+    def test_channel_persists_feishu_domain_from_config(self):
+        ch = _make_channel(domain="feishu")
+        assert ch.config.domain == "feishu"