added formulas

api/tests/test_api.py

@@ -147,4 +147,7 @@ def test_manual_link_budget_endpoint() -> None:
     assert data["fspl_db"] > 0
     assert "link_viable" in data
     assert data["fresnel_quality"] in {"clear", "partial", "blocked"}
+    assert "propagation_model_loss_db" in data
+    assert "propagation_excess_db" in data
+    assert "knife_edge_diffraction_db" in data
     assert "data_sources" in data