add projekt cpn support

tests/test_app.py

@@ -128,3 +128,38 @@ def test_migration_runner_creates_registry_without_legacy_migrations(tmp_path):
         assert migrate_database() == []
         assert "schema_migration" in inspect(db.engine).get_table_names()
         assert migrate_database() == []
+
+def test_global_vat_override_changes_50_percent_deduction(tmp_path):
+    from decimal import Decimal
+    from datetime import date
+    from app.extensions import db
+    from app.models import AppSetting
+    from app.vat import effective_vat_rate
+
+    app = make_app(tmp_path, "global-vat.db")
+    with app.app_context():
+        for key, value in {
+            "global_vat_override_enabled": "1",
+            "global_vat_override_name": "CPN",
+            "global_vat_override_rate": "8",
+            "global_vat_override_start": "2026-07-01",
+            "global_vat_override_end": "2026-07-31",
+        }.items():
+            db.session.merge(AppSetting(key=key, value=value))
+        db.session.commit()
+        rate = effective_vat_rate(Decimal("23"), date(2026, 7, 15))
+        result = calculate_costs(Decimal("108"), rate, 50)
+        assert rate == Decimal("8")
+        assert result["net"] == Decimal("100.00")
+        assert result["vat"] == Decimal("8.00")
+        assert result["deductible_vat"] == Decimal("4.00")
+        assert effective_vat_rate(Decimal("23"), date(2026, 8, 1)) == Decimal("23")
+
+
+def test_only_admin_can_change_global_vat(tmp_path):
+    app = make_app(tmp_path, "global-vat-auth.db")
+    client = app.test_client()
+    client.post('/login', data={'email':'admin@example.com','password':'admin123!'})
+    response = client.post('/admin/global-vat', data={'enabled':'on','name':'CPN','rate':'8','start':'2026-07-01','end':'2026-07-31'}, headers={'X-Requested-With':'XMLHttpRequest'})
+    assert response.status_code == 200
+    assert response.json['ok'] is True