fix: remove numpy dependency from test_memory_embeddings

Use MagicMock to simulate .tolist() instead of importing numpy,
which is not in the test dependencies.

Fixes broken unit test on main.

tests/unit/test_memory_embeddings.py

@@ -112,10 +112,10 @@ class TestEmbedText:
         assert len(vec) == 128  # hash fallback dimension
 
     def test_uses_model_when_available(self):
-        import numpy as np
-
+        mock_encoding = MagicMock()
+        mock_encoding.tolist.return_value = [0.1, 0.2, 0.3]
         mock_model = MagicMock()
-        mock_model.encode.return_value = np.array([0.1, 0.2, 0.3])
+        mock_model.encode.return_value = mock_encoding
         emb.EMBEDDING_MODEL = mock_model
 
         result = embed_text("test")