sync(server-release): 从 main 同步逻辑改动（不含 API 格式变更）

同步内容:
- knowledge/manager.py: VLM max_tokens 512→2048 + reasoning_content fallback
- services/feedback.py: FAQ max_tokens 200→512
- services/session.py: 消息排序增加 id DESC 次级排序
- knowledge/image_cleanup.py: 新增图片/VLM缓存孤儿文件清理模块
- knowledge/collection.py: 集合删除时清理孤儿文件 + list_collections 磁盘扫描策略
- knowledge/document.py: 文档删除时清理孤儿文件
- api/chat_routes.py: 新增 _rescue_bm25_divergence 函数（BM25-CE分歧救援）
- core/intent_analyzer.py: 使用 get_intent_client 专用客户端 + 移除短追问缓存跳过逻辑
- cleanup_orphans.py: 独立孤儿文件清理脚本

knowledge/document.py

@@ -72,6 +72,18 @@ class DocumentMixin:
         except Exception as e:
             logger.warning(f"清理版本记录失败: {e}")
 
+        # 清理不再被引用的图片和 VLM 缓存文件
+        try:
+            from knowledge.image_cleanup import cleanup_image_orphans
+            cleanup_result = cleanup_image_orphans(self, collections=[kb_name])
+            if cleanup_result['deleted_images'] or cleanup_result['deleted_caches']:
+                logger.info(
+                    f"清理孤儿文件: {cleanup_result['deleted_images']} 图片 + "
+                    f"{cleanup_result['deleted_caches']} VLM缓存"
+                )
+        except Exception as e:
+            logger.warning(f"清理孤儿文件失败: {e}")
+
         logger.info(f"从 {kb_name} 删除文档: {filename}, 片段数: {deleted}")
         return deleted