refactor: remove legacy assistant compatibility

backend/tests/test_fixed_speech_playback.py

@@ -65,7 +65,7 @@ class FixedSpeechPlaybackTest(unittest.IsolatedAsyncioTestCase):
 
     async def test_realtime_end_ignores_unrelated_speech_boundaries(self):
         graph = {
-            "specVersion": 3,
+            "specVersion": 4,
             "settings": {},
             "nodes": [
                 {"id": "start", "type": "start", "data": {}},
@@ -144,7 +144,7 @@ class FixedSpeechPlaybackTest(unittest.IsolatedAsyncioTestCase):
 
     async def test_realtime_confirmation_is_appended_without_running_model(self):
         graph = {
-            "specVersion": 3,
+            "specVersion": 4,
             "settings": {},
             "nodes": [
                 {