feat(cron+tests): extend origin fallback to email/dingtalk/qqbot + fix Weixin test mocks

Cron origin fallback extension (builds on #9193's _HOME_TARGET_ENV_VARS):
adds the three remaining origin-fallback-eligible platforms that have
home channel env vars configured in gateway/config.py but use non-generic
env var names:

- email    → EMAIL_HOME_ADDRESS   (non-standard suffix)
- dingtalk → DINGTALK_HOME_CHANNEL
- qqbot    → QQ_HOME_CHANNEL      (non-standard prefix: QQ_ not QQBOT_)

Picks up the completeness intent of @Xowiek's PR #11317 using the
architecturally-correct dict-based lookup from #9193, so platforms with
non-standard env var names actually resolve instead of silently missing.
Extended the parametrized regression test to cover the new three.

Weixin test mock alignment (builds on #10091's _send_session split):
Three test sites added in Batch 1 (TestWeixinSendImageFileParameterName)
and Batch 3 (TestWeixinVoiceSending) mocked only adapter._session, but
#10091 switched the send paths to check self._send_session. Added the
companion setter so the tests stay green with the session split in place.

tests/gateway/test_weixin.py

@@ -527,6 +527,7 @@ class TestWeixinSendImageFileParameterName:
         """Verify send_image_file accepts image_path and forwards to send_document."""
         adapter = _make_adapter()
         adapter._session = object()
+        adapter._send_session = adapter._session
         adapter._token = "test-token"
 
         send_document_mock.return_value = weixin.SendResult(success=True, message_id="test-id")
@@ -554,6 +555,7 @@ class TestWeixinSendImageFileParameterName:
         """Verify send_image_file works with minimal required params."""
         adapter = _make_adapter()
         adapter._session = object()
+        adapter._send_session = adapter._session
         adapter._token = "test-token"
 
         send_document_mock.return_value = weixin.SendResult(success=True, message_id="test-id")
@@ -578,6 +580,7 @@ class TestWeixinVoiceSending:
     def _connected_adapter(self) -> WeixinAdapter:
         adapter = _make_adapter()
         adapter._session = object()
+        adapter._send_session = adapter._session
         adapter._token = "test-token"
         adapter._base_url = "https://weixin.example.com"
         adapter._token_store.get = lambda account_id, chat_id: "ctx-token"