KnowledgeFS QA synthetic corpus

Unique marker: KF_QA_MARKER_20260811_X9Z
The marker is used only to verify parsing, indexing, retrieval, citations, and deletion cleanup.

中文校验：知识库测试标记是 KF_QA_MARKER_20260811_X9Z。
English check: the KnowledgeFS test marker is KF_QA_MARKER_20260811_X9Z.

