fix w kalkulacji last price

tests/test_app.py

@@ -349,3 +349,16 @@ def test_orlen_comparison_filters_to_one_fuel(tmp_path):
     assert '4.5000' in html
     assert '4.1000' in html
     assert '>DIESEL</td>' not in html
+
+
+def test_last_price_uses_only_non_deductible_vat():
+    from app.domain.costs import calculate_net_price_costs
+    result = calculate_net_price_costs(5.484, 23, 50)
+    assert round(float(result["invoice_gross"]), 4) == 6.7453
+    assert round(float(result["effective_cost"]), 4) == 6.1147
+
+
+def test_last_price_zero_and_full_vat_deduction():
+    from app.domain.costs import calculate_net_price_costs
+    assert round(float(calculate_net_price_costs(10, 23, 0)["effective_cost"]), 2) == 12.30
+    assert round(float(calculate_net_price_costs(10, 23, 100)["effective_cost"]), 2) == 10.00