feat(knowledge): 任务队列、独立 worker 与 pgvector 向量索引

知识处理改为数据库任务队列，独立 worker 做切块与向量化，失败可重试。

backend/scripts/preload_models.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+import os
+import sys
+import logging
+
+# Add the app directory to the Python path
+sys.path.insert(0, '/app')
+
+# Configure logging
+logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
+logger = logging.getLogger(__name__)
+
+def preload_agno_embedder():
+    """Preload the fastembed model agno embeds with"""
+    try:
+        from agno.embedder.fastembed import FastEmbedEmbedder
+        
+        # Get model ID from environment or use default
+        model_id = os.getenv("FASTEMBED_MODEL", "BAAI/bge-small-en-v1.5")
+        
+        logger.info(f"Preloading Agno FastEmbedEmbedder: {model_id}")
+        
+        # Initialize the embedder
+        embedder = FastEmbedEmbedder(id=model_id)
+        
+        # Test embedding using the correct API method
+        test_text = "Test embedding for Agno embedder initialization."
+        embedding = embedder.get_embedding(test_text)
+        
+        logger.info(f"Successfully preloaded Agno embedder {model_id}. Embedding dimension: {len(embedding)}")
+        
+        # Clean up
+        del embedder
+        del embedding
+        
+        return True
+        
+    except Exception as e:
+        logger.error(f"Failed to preload Agno embedder: {str(e)}")
+        return False
+
+def main():
+    """Warm the embedding model cache so the first request does not pay for the download"""
+    logger.info("Starting model preloading process...")
+
+    if not preload_agno_embedder():
+        logger.error("Model preloading failed")
+        return 1
+
+    logger.info("All models preloaded successfully!")
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(main())