fix(backend): add embed_query method to EmbeddingFunctionWrapper for ChromaDB query

ChromaDB 1.5.8 calls embed_query() during collection.query(), but the wrapper only implemented __call__ (used by collection.add()). Added embed_query() as alias and refactored to shared _embed() method.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/app/core/database.py

@@ -14,6 +14,12 @@ class _EmbeddingFunctionWrapper:
         return "custom_embedding_wrapper"
 
     def __call__(self, input):
+        return self._embed(input)
+
+    def embed_query(self, input):
+        return self._embed(input)
+
+    def _embed(self, texts):
         from app.services.embedding_client import EmbeddingClient
         import asyncio
         from concurrent.futures import ThreadPoolExecutor
@@ -28,7 +34,7 @@ class _EmbeddingFunctionWrapper:
                 loop.close()
 
         with ThreadPoolExecutor(max_workers=1) as executor:
-            return executor.submit(_run_in_thread, input).result()
+            return executor.submit(_run_in_thread, texts).result()
 
 
 def get_embedding_function_settings(settings):