Embeddings API scores (#671)

- Put scores in all responses
- Remove unused 'middle' vector layer. Vector of texts -> vector of (vector embedding)

tests/integration/test_graph_rag_streaming_integration.py

@@ -8,6 +8,7 @@ response delivery through the complete pipeline.
 import pytest
 from unittest.mock import AsyncMock, MagicMock
 from trustgraph.retrieval.graph_rag.graph_rag import GraphRag
+from trustgraph.schema import EntityMatch, Term, IRI
 from tests.utils.streaming_assertions import (
     assert_streaming_chunks_valid,
     assert_rag_streaming_chunks,
@@ -33,7 +34,7 @@ class TestGraphRagStreaming:
         """Mock graph embeddings client"""
         client = AsyncMock()
         client.query.return_value = [
-            "http://trustgraph.ai/e/machine-learning",
+            EntityMatch(entity=Term(type=IRI, iri="http://trustgraph.ai/e/machine-learning"), score=0.95),
         ]
         return client