fix: count all documents for homepage stats, not just knowledge_base type

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/api/analytics.py

@@ -243,10 +243,8 @@ async def get_platform_stats(
         total_users = db.query(func.count(User.id)).scalar() or 0
         active_users = max(users_with_sessions, users_with_documents, total_users)
         
-        # 知识文档数（知识库中的文档）
-        knowledge_documents = db.query(func.count(Document.id)).filter(
-            Document.source_type == "knowledge_base"
-        ).scalar() or 0
+        # 知识文档数（所有文档）
+        knowledge_documents = db.query(func.count(Document.id)).scalar() or 0
         
         # 问答对话数（所有用户消息）
         qa_dialogues = db.query(func.count(ChatMessage.id)).filter(