fix(backend): Refactor OIDC callback and auth dependency to correctly handle cookies and prefix all API routes with /api/v1.

backend/tests/api/test_agent.py

@@ -21,7 +21,7 @@ def auth_header(mock_user):
 
 def test_stream_agent_unauthorized():
     """Test that streaming requires authentication."""
-    response = client.post("/chat/stream", json={"message": "hello"})
+    response = client.post("/api/v1/chat/stream", json={"message": "hello"})
     assert response.status_code == 401
 
 @pytest.mark.asyncio
@@ -52,7 +52,7 @@ async def test_stream_agent_success(auth_header, mock_user):
         mock_session.get.return_value = mock_conv
         
         # Using TestClient with a stream context
-        with client.stream("POST", "/chat/stream", 
+        with client.stream("POST", "/api/v1/chat/stream", 
                           json={"message": "hello", "thread_id": "t1"}, 
                           headers=auth_header) as response:
             assert response.status_code == 200