fix: add thread-safe write lock to ChromaDB operations

src/core/search.py

@@ -75,14 +75,15 @@ class Searcher:
         return sorted(sources)
 
     def delete_by_source(self, file_name: str) -> bool:
-        """按文件名删除文档."""
+        """按文件名删除文档 (线程安全)."""
         try:
-            existing = self.collection.get(
-                where={"source_file": file_name}
-            )
-            if existing and existing["ids"]:
-                self.collection.delete(ids=existing["ids"])
-                return True
+            with self.db.write_lock:
+                existing = self.collection.get(
+                    where={"source_file": file_name}
+                )
+                if existing and existing["ids"]:
+                    self.collection.delete(ids=existing["ids"])
+                    return True
         except Exception:
             pass
         return False