fix(backend): wrap embedding function for ChromaDB 0.4.22 compatibility

- Add _EmbeddingFunctionWrapper class with __call__(self, input) signature

- Use ThreadPoolExecutor to run async embed in isolated thread with fresh event loop

- Fixes asyncio.run() cannot be called from a running event loop

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

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

backend/app/core/database.py

@@ -1,10 +1,42 @@
 from pathlib import Path
 
 import chromadb
+from typing import Callable, Optional
 
 from app.core.config import get_settings
 
 
+class _EmbeddingFunctionWrapper:
+    def __init__(self, settings):
+        self.settings = settings
+
+    def __call__(self, input):
+        from app.services.embedding_client import EmbeddingClient
+        import asyncio
+        from concurrent.futures import ThreadPoolExecutor
+
+        def _run_in_thread(texts):
+            client = EmbeddingClient(self.settings)
+            loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(loop)
+            try:
+                return loop.run_until_complete(client.embed(texts))
+            finally:
+                loop.close()
+
+        with ThreadPoolExecutor(max_workers=1) as executor:
+            return executor.submit(_run_in_thread, input).result()
+
+
+def get_embedding_function_settings(settings):
+    """Return a synchronous wrapper suitable for embedding functions in ChromaDB."""
+    # Lazy import to avoid import-time side effects in tests
+    try:
+        return _EmbeddingFunctionWrapper(settings)
+    except Exception:
+        return None
+
+
 def get_chroma_client() -> chromadb.Client:
     settings = get_settings()
     persist_dir = Path(settings.chroma_db_path)
@@ -12,5 +44,7 @@ def get_chroma_client() -> chromadb.Client:
     return chromadb.PersistentClient(path=str(persist_dir))
 
 
-def get_or_create_collection(client: chromadb.Client, name: str):
+def get_or_create_collection(client: chromadb.Client, name: str, embedding_function: Optional[Callable] = None):
+    if embedding_function is not None:
+        return client.get_or_create_collection(name=name, embedding_function=embedding_function)
     return client.get_or_create_collection(name=name)