perf: switch Qdrant to AsyncQdrantClient with explicit timeout

Every vector call ran on the sync QdrantClient inside async wrapper
methods, blocking the FastAPI event loop per Qdrant round-trip. The
wrapper now holds an AsyncQdrantClient (timeout via QDRANT_TIMEOUT,
default 30s) and awaits all client calls; the wrapper API is unchanged.

Call sites off the wrapper were fixed too: the HybridRAG document leg
now uses the async search_vectors wrapper instead of the deprecated raw
client.search (also fixing its call to the nonexistent ollama.embed_text
which made the leg permanently report 'failed'), the health check awaits
get_collections, and document_sync's raw delete/upsert calls are awaited
(routed through wrappers in the next commit).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QbFZyDvYksazX6nYQYZ67L

tests/test_integration.py

@@ -148,7 +148,7 @@ class TestQdrantIntegration:
         collection_name = qdrant_client.get_collection_name(test_user)
         await qdrant_client.ensure_collection(collection_name)
 
-        collections = qdrant_client.client.get_collections()
+        collections = await qdrant_client.client.get_collections()
         collection_names = [c.name for c in collections.collections]
 
         assert collection_name in collection_names