fix(withdraw): OPPO channel_id 改用管理台登记的 push_oplus_category_content

上一提交(0921cb8)误用占位值 shagua_wallet, 真机会不展示; 改为用户在 OPPO 管理台建的通信 ID。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_oppo_push.py

@@ -68,7 +68,7 @@ def test_success_flow(monkeypatch) -> None:
     assert msg["notification"]["title"] == "标题"
     assert msg["notification"]["content"] == "内容"
     # channel_id 必带(默认 shagua_wallet); category 默认空 → 不带
-    assert msg["notification"]["channel_id"] == "shagua_wallet"
+    assert msg["notification"]["channel_id"] == "push_oplus_category_content"
     assert "category" not in msg["notification"]