Backend: Mindestbestand je Lagerort für Produkte und Gruppen

Zusaetzlich zum globalen Mindestbestand: je Produkt und je Gruppe laesst sich pro
Lagerort ein Mindestbestand (in Artikeleinheiten) hinterlegen.
- Neue Tabellen product_location_min_stock / group_location_min_stock.
- PUT /products/{id}/location-min-stock und /groups/{id}/location-min-stock
  ersetzen die Eintraege; Produkt-/Gruppen-Ausgabe liefert sie mit.
- Neue Einkaufsliste GET /shopping-list/by-location: Bedarfe je Ort (Produkte +
  Gruppen), Bestand-am-Ort gegen Mindestbestand-am-Ort.
- Helfer location_stock_base (Bestand je Ort). 4 neue Tests, Suite 144 gruen.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/routers/groups.py

@@ -3,7 +3,7 @@ from sqlalchemy.orm import Session
 
 from ..database import get_db
 from ..deps import get_current_user, require_admin
-from ..models import Barcode, Group, Product, User
+from ..models import Barcode, Group, GroupLocationMinStock, Location, Product, User
 from ..schemas import (
     BarcodeCreate,
     BarcodeNoteUpdate,
@@ -11,6 +11,8 @@ from ..schemas import (
     GroupCreate,
     GroupOut,
     GroupUpdate,
+    LocationMinStockIn,
+    LocationMinStockOut,
     ProductBarcodeOut,
 )
 from ..services.conversion import BASE_OF_KIND
@@ -76,6 +78,15 @@ def _group_to_out(db: Session, group: Group) -> GroupOut:
         out.kind = unit.kind.value
     else:
         out.stock = float(sum(current_stock(db, p.id) for p in products))
+
+    out.location_min_stocks = [
+        LocationMinStockOut(
+            location_id=e.location_id,
+            location_name=e.location.name if e.location else None,
+            min_stock=e.min_stock,
+        )
+        for e in sorted(group.location_min_stocks, key=lambda x: x.id)
+    ]
     return out
 
 
@@ -87,6 +98,38 @@ def list_groups(
     return [_group_to_out(db, g) for g in groups]
 
 
+@router.put("/{group_id}/location-min-stock", response_model=GroupOut)
+def set_group_location_min_stock(
+    group_id: int,
+    payload: list[LocationMinStockIn],
+    db: Session = Depends(get_db),
+    _: User = Depends(require_admin),
+) -> GroupOut:
+    """Gruppen-Mindestbestände je Lagerort ersetzen (Menge 0 = Eintrag entfällt)."""
+    group = db.get(Group, group_id)
+    if group is None:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "Gruppe nicht gefunden")
+
+    db.query(GroupLocationMinStock).filter(
+        GroupLocationMinStock.group_id == group_id
+    ).delete()
+    gesehen: set[int] = set()
+    for eintrag in payload:
+        if eintrag.min_stock <= 0 or eintrag.location_id in gesehen:
+            continue
+        if db.get(Location, eintrag.location_id) is None:
+            raise HTTPException(status.HTTP_404_NOT_FOUND, "Lagerort nicht gefunden")
+        gesehen.add(eintrag.location_id)
+        db.add(GroupLocationMinStock(
+            group_id=group_id,
+            location_id=eintrag.location_id,
+            min_stock=eintrag.min_stock,
+        ))
+    db.commit()
+    db.refresh(group)
+    return _group_to_out(db, group)
+
+
 @router.post("", response_model=GroupOut, status_code=status.HTTP_201_CREATED)
 def create_group(
     payload: GroupCreate,