refactor: Tilgungsplan-Helfer schedule_for, Kredit-Laufzeit 1–1200 Monate (A14-T5)

- Neuer schedule_for() in app/engine/loans.py: vereinheitlicht Tilgungsplan-Erstellung
- Laufzeit-Validierung in LoanIn und LoanPatch: 1–1200 Monate
- Aufrufstellen aktualisiert (routers/planning.py, services/breakdown.py,
  services/projection_service.py, services/planning_chart.py)
- Keine direkten loan_schedule(Decimal(...)) Aufrufe außerhalb engine/loans.py mehr
- Tests für schedule_for und Laufzeit-Grenzen (1, 1200, sowie 0/-5/1201 Ablehnung)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

finance/tests/test_loans.py

@@ -27,3 +27,21 @@ def test_bullet_loan():
     assert all(i.principal == 0 for i in plan[:-1])
     assert plan[-1].principal == Decimal("10000")
     assert plan[-1].remaining == Decimal("0.00")
+
+
+def test_schedule_for_entspricht_loan_schedule():
+    from types import SimpleNamespace
+    from app.engine.loans import schedule_for
+    kredit = SimpleNamespace(principal="1200.00", annual_rate_pct="3.00", term_months=12,
+                             payout_date=date(2030, 1, 31), repayment_type="annuity")
+    assert schedule_for(kredit) == loan_schedule(Decimal("1200.00"), Decimal("3.00"), 12,
+                                                 date(2030, 1, 31), "annuity")
+
+
+def test_keine_manuelle_tilgungsplan_konvertierung_mehr():
+    from pathlib import Path
+    app_dir = Path(__file__).resolve().parent.parent / "app"
+    engine_loans = app_dir / "engine" / "loans.py"
+    treffer = [str(p.relative_to(app_dir)) for p in app_dir.rglob("*.py")
+               if p != engine_loans and "loan_schedule(Decimal(" in p.read_text()]
+    assert treffer == []

finance/tests/test_planning_api.py

@@ -2,6 +2,8 @@ from datetime import date
 from decimal import Decimal
 from itertools import count
 
+import pytest
+
 from app.models.tables import Account, Category, RecurringItem, Transaction
 from app.services.suggestions import _Series, _try_merge, suggest_recurring
 
@@ -368,3 +370,25 @@ def test_suggest_volatilitaetshinweis_bei_abgetrennter_neuester_buchung(db):
     assert len(out) == 1
     assert out[0]["amount"] == Decimal("-200.00")  # Betrag NICHT durch die 600er-Buchung verfaelscht
     assert "schwanken" in out[0]["hinweis"].lower()
+
+
+# ----------------------------------------------------------- Ausbaustufe 14: Task 5
+KREDIT = {"name": "Laufzeit-Test", "principal": "1000.00", "annual_rate_pct": "2.00",
+          "payout_date": "2030-01-01", "repayment_type": "annuity"}
+
+
+@pytest.mark.parametrize("laufzeit", [0, -5, 1201])
+def test_kredit_laufzeit_ausserhalb_1_bis_1200(client, laufzeit):
+    r = client.post("/api/loans", headers=H, json={**KREDIT, "term_months": laufzeit})
+    assert r.status_code == 422
+
+
+def test_kredit_laufzeit_grenzen_und_patch(client):
+    a = client.post("/api/loans", headers=H, json={**KREDIT, "term_months": 1})
+    b = client.post("/api/loans", headers=H, json={**KREDIT, "name": "L2", "term_months": 1200})
+    assert (a.status_code, b.status_code) == (201, 201)
+    url = f"/api/loans/{a.json()['id']}"
+    assert client.patch(url, headers=H, json={"term_months": 0}).status_code == 422
+    assert client.patch(url, headers=H, json={"term_months": 1201}).status_code == 422
+    r = client.patch(url, headers=H, json={"term_months": 1200})
+    assert r.status_code == 200 and r.json()["term_months"] == 1200