Verwaltbare Einheiten mit Umrechnung + Chargen bearbeiten + gezieltes Auslagern

Einheiten (neu):
- Tabelle units (name, kind=count|weight|volume, factor, is_builtin); eingebaut
  Stueck/Gramm/Kilogramm/Milliliter/Liter, Admin kann eigene anlegen (z.B. Pfund=500g).
- Bestaende bleiben intern in kanonischer Basis (Stueck/Gramm/Milliliter);
  Product.display_unit_id und Group.min_stock_unit_id als nullable FKs.
- Neuer Umrechnungs-Service (services/conversion.py) ersetzt die feste Einheitenlogik;
  Ein-/Auslagern und Gruppen-Mindestbestand rechnen ueber den Faktor.
- Gruppen-Mindestbestand mit Einheit; Gruppenbestand summiert nur Produkte
  passender Art. Neue Verwaltungsseite "Einheiten" (Admin).
- Schonende Migration beim Start: ADD COLUMN IF NOT EXISTS (Postgres), damit
  bestehende Installationen ihre Daten behalten.

Chargen:
- PATCH /lots/{id} und DELETE /lots/{id}: Menge/MHD korrigieren, Charge loeschen
  (wird als Korrektur-Bewegung protokolliert). Bearbeitung im Produktdetail.

Auslagern:
- Optionales lot_id: gezielt aus einer bestimmten Charge/MHD abbuchen statt FEFO;
  Auswahl-Dropdown in der Auslagern-Seite.

Sonstiges: Roadmap aktualisiert, Tests fuer die Umrechnung.

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

backend/app/routers/stock.py

@@ -4,7 +4,7 @@ from sqlalchemy.orm import Session
 from ..crud import resolve_product
 from ..database import get_db
 from ..deps import get_current_user
-from ..models import Lot, User
+from ..models import Lot, Movement, MovementType, User
 from ..schemas import (
     BatchCheckInRequest,
     BatchCheckInResponse,
@@ -13,9 +13,16 @@ from ..schemas import (
     CheckOutRequest,
     CheckOutResponse,
     LotOut,
+    LotUpdate,
+)
+from ..services.conversion import ConversionError
+from ..services.stock import (
+    StockError,
+    check_in,
+    check_out,
+    check_out_lot,
+    current_stock,
 )
-from ..services.stock import StockError, check_in, check_out, current_stock
-from ..services.units import UnitError
 
 router = APIRouter(tags=["stock"])
 
@@ -38,7 +45,7 @@ def stock_checkin(
             user=user,
             note=payload.note,
         )
-    except UnitError as exc:
+    except ConversionError as exc:
         raise HTTPException(status.HTTP_400_BAD_REQUEST, str(exc)) from exc
     db.commit()
     db.refresh(lot)
@@ -74,7 +81,7 @@ def stock_checkin_batch(
                     note=payload.note,
                 )
             )
-    except UnitError as exc:
+    except ConversionError as exc:
         db.rollback()
         raise HTTPException(status.HTTP_400_BAD_REQUEST, str(exc)) from exc
     db.commit()
@@ -94,15 +101,31 @@ def stock_checkout(
 ) -> CheckOutResponse:
     product = resolve_product(db, payload.product_id, payload.barcode)
     try:
-        affected = check_out(
-            db,
-            product=product,
-            quantity=payload.quantity,
-            unit=payload.unit,
-            user=user,
-            note=payload.note,
-        )
-    except UnitError as exc:
+        if payload.lot_id is not None:
+            lot = db.get(Lot, payload.lot_id)
+            if lot is None or lot.product_id != product.id:
+                raise HTTPException(
+                    status.HTTP_404_NOT_FOUND, "Charge gehört nicht zu diesem Produkt"
+                )
+            affected = check_out_lot(
+                db,
+                product=product,
+                lot=lot,
+                quantity=payload.quantity,
+                unit=payload.unit,
+                user=user,
+                note=payload.note,
+            )
+        else:
+            affected = check_out(
+                db,
+                product=product,
+                quantity=payload.quantity,
+                unit=payload.unit,
+                user=user,
+                note=payload.note,
+            )
+    except ConversionError as exc:
         raise HTTPException(status.HTTP_400_BAD_REQUEST, str(exc)) from exc
     except StockError as exc:
         raise HTTPException(status.HTTP_409_CONFLICT, str(exc)) from exc
@@ -122,3 +145,63 @@ def list_lots(
     if product_id is not None:
         query = query.filter(Lot.product_id == product_id)
     return query.order_by(Lot.best_before.is_(None), Lot.best_before).all()
+
+
+@router.patch("/lots/{lot_id}", response_model=LotOut)
+def update_lot(
+    lot_id: int,
+    payload: LotUpdate,
+    db: Session = Depends(get_db),
+    user: User = Depends(get_current_user),
+) -> Lot:
+    """Korrigiert eine Charge (Menge in Basiseinheiten, MHD, Lagerort)."""
+    lot = db.get(Lot, lot_id)
+    if lot is None:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "Charge nicht gefunden")
+
+    data = payload.model_dump(exclude_unset=True)
+    old_quantity = lot.quantity
+    for field, value in data.items():
+        setattr(lot, field, value)
+
+    delta = lot.quantity - old_quantity
+    if abs(delta) > 1e-9:
+        db.add(
+            Movement(
+                product_id=lot.product_id,
+                lot_id=lot.id,
+                user_id=user.id,
+                type=MovementType.adjust,
+                quantity=delta,
+                unit_used="base",
+                note="Charge korrigiert",
+            )
+        )
+    db.commit()
+    db.refresh(lot)
+    return lot
+
+
+@router.delete("/lots/{lot_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_lot(
+    lot_id: int,
+    db: Session = Depends(get_db),
+    user: User = Depends(get_current_user),
+) -> None:
+    """Entfernt eine Charge komplett aus dem Bestand."""
+    lot = db.get(Lot, lot_id)
+    if lot is None:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "Charge nicht gefunden")
+    db.add(
+        Movement(
+            product_id=lot.product_id,
+            lot_id=None,
+            user_id=user.id,
+            type=MovementType.adjust,
+            quantity=-lot.quantity,
+            unit_used="base",
+            note="Charge gelöscht",
+        )
+    )
+    db.delete(lot)
+    db.commit()