feat: allow a honey batch to be split across multiple storage containers

A batch that doesn't fit in one container (e.g. 125 kg across 5 x 25 kg
buckets) had no way to be represented - HoneyBatch.storageContainerId
is a single nullable FK. Adds HoneyBatchContainerAllocation as an
additive join table (container + amount per batch), independent of the
existing single-container/relocate() flow which still covers the
simple one-container case unchanged.

- GET/PUT/DELETE /honey-batches/:id/containers[/:containerId], reusing
  the existing honey-batches:relocate permission.
- Assigning a container is an upsert (@@unique on batch+container), and
  the total assigned is validated against the batch's own amount when
  known.
- New "Aufteilung auf mehrere Behälter" card on the honey batch detail
  page, alongside (not replacing) the existing storage card.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

ApiCore-Frontend/src/app/(app)/honey-batches/[id]/honey-batch-container-allocations-card.tsx

@@ -0,0 +1,190 @@
+"use client";
+
+import { FormEvent, useState } from "react";
+import { Trash2 } from "lucide-react";
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import { toast } from "sonner";
+import {
+  fetchHoneyBatchContainerAllocations,
+  removeHoneyBatchContainerAllocation,
+  setHoneyBatchContainerAllocation,
+} from "@/lib/honey-batches/api";
+import { HoneyBatch } from "@/lib/honey-batches/types";
+import { fetchStorageContainers } from "@/lib/storage/api";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { EmptyState } from "@/components/empty-state";
+import { Boxes } from "lucide-react";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+
+// Additive to HoneyBatchStorageCard's single-container "Umlagern" flow above
+// it on the page - covers a batch too large for one container (e.g. 125 kg
+// split across 5 x 25 kg buckets), which a single storageContainerId can't
+// represent.
+export function HoneyBatchContainerAllocationsCard({ honeyBatch }: { honeyBatch: HoneyBatch }) {
+  const queryClient = useQueryClient();
+  const [storageContainerId, setStorageContainerId] = useState("");
+  const [amount, setAmount] = useState("");
+  const [error, setError] = useState<string | null>(null);
+
+  const { data: containers } = useQuery({
+    queryKey: ["storage-containers"],
+    queryFn: fetchStorageContainers,
+  });
+
+  const {
+    data: allocations,
+    isLoading,
+  } = useQuery({
+    queryKey: ["honey-batches", honeyBatch.id, "containers"],
+    queryFn: () => fetchHoneyBatchContainerAllocations(honeyBatch.id),
+  });
+
+  const assignMutation = useMutation({
+    mutationFn: (input: { storageContainerId: string; amount: number }) =>
+      setHoneyBatchContainerAllocation(honeyBatch.id, input.storageContainerId, input.amount),
+    onSuccess: () => {
+      void queryClient.invalidateQueries({
+        queryKey: ["honey-batches", honeyBatch.id, "containers"],
+      });
+      setStorageContainerId("");
+      setAmount("");
+      setError(null);
+    },
+    onError: () => {
+      setError("Zuweisung konnte nicht gespeichert werden. Übersteigt die Menge die Charge?");
+    },
+  });
+
+  const removeMutation = useMutation({
+    mutationFn: (containerId: string) =>
+      removeHoneyBatchContainerAllocation(honeyBatch.id, containerId),
+    onSuccess: () => {
+      void queryClient.invalidateQueries({
+        queryKey: ["honey-batches", honeyBatch.id, "containers"],
+      });
+      toast.success("Zuweisung entfernt");
+    },
+    onError: () => toast.error("Zuweisung konnte nicht entfernt werden"),
+  });
+
+  function handleSubmit(event: FormEvent<HTMLFormElement>) {
+    event.preventDefault();
+    setError(null);
+    if (!storageContainerId) {
+      setError("Bitte einen Lagerbehälter auswählen.");
+      return;
+    }
+    const parsedAmount = Number(amount);
+    if (!amount || parsedAmount <= 0) {
+      setError("Bitte eine Menge größer als 0 angeben.");
+      return;
+    }
+    assignMutation.mutate({ storageContainerId, amount: parsedAmount });
+  }
+
+  const totalAllocated = (allocations ?? []).reduce((sum, a) => sum + a.amount, 0);
+
+  return (
+    <Card>
+      <CardHeader>
+        <CardTitle>Aufteilung auf mehrere Behälter</CardTitle>
+      </CardHeader>
+      <CardContent className="flex flex-col gap-4 text-sm">
+        <p className="text-xs text-muted-foreground">
+          Für Chargen, die nicht in einen einzigen Behälter passen (z. B. 125 kg auf 5 Eimer à 25
+          kg). Unabhängig vom Lagerbehälter oben.
+        </p>
+
+        {honeyBatch.amount !== null ? (
+          <p className="text-muted-foreground">
+            Zugewiesen: {totalAllocated} kg von {honeyBatch.amount} kg
+          </p>
+        ) : null}
+
+        {isLoading ? <p className="text-muted-foreground">Lädt…</p> : null}
+        {!isLoading && (!allocations || allocations.length === 0) ? (
+          <EmptyState
+            icon={Boxes}
+            title="Noch keine Aufteilung"
+            description="Weise dieser Charge unten mehrere Behälter mit jeweiliger Menge zu."
+          />
+        ) : null}
+        {allocations?.map((allocation) => (
+          <div
+            key={allocation.id}
+            className="flex items-center justify-between rounded-md border p-3"
+          >
+            <div>
+              <p className="font-medium">
+                {allocation.storageContainer.code}
+                {allocation.storageContainer.location
+                  ? ` · ${allocation.storageContainer.location}`
+                  : ""}
+              </p>
+              <p className="text-muted-foreground">{allocation.amount} kg</p>
+            </div>
+            <Button
+              type="button"
+              variant="ghost"
+              size="icon"
+              disabled={removeMutation.isPending}
+              onClick={() => removeMutation.mutate(allocation.storageContainerId)}
+              aria-label="Zuweisung entfernen"
+            >
+              <Trash2 className="size-4" />
+            </Button>
+          </div>
+        ))}
+
+        <form className="flex flex-col gap-3 border-t border-border/60 pt-4" onSubmit={handleSubmit}>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="allocation-container">Behälter</Label>
+            <Select
+              value={storageContainerId}
+              onValueChange={(value) => setStorageContainerId(value ?? "")}
+            >
+              <SelectTrigger id="allocation-container">
+                <SelectValue placeholder="Lagerbehälter wählen" />
+              </SelectTrigger>
+              <SelectContent>
+                {containers?.map((container) => (
+                  <SelectItem key={container.id} value={container.id}>
+                    {container.code}
+                    {container.location ? ` · ${container.location}` : ""}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+          <div className="flex flex-col gap-2">
+            <Label htmlFor="allocation-amount">Menge (kg)</Label>
+            <Input
+              id="allocation-amount"
+              type="number"
+              inputMode="decimal"
+              value={amount}
+              onChange={(event) => setAmount(event.target.value)}
+            />
+          </div>
+          {error ? (
+            <p role="alert" className="text-sm text-destructive">
+              {error}
+            </p>
+          ) : null}
+          <Button type="submit" variant="outline" disabled={assignMutation.isPending}>
+            {assignMutation.isPending ? "Wird zugewiesen…" : "Behälter zuweisen"}
+          </Button>
+        </form>
+      </CardContent>
+    </Card>
+  );
+}

ApiCore-Frontend/src/app/(app)/honey-batches/[id]/page.tsx

@@ -11,6 +11,7 @@ import { QrCodeDialog } from "@/components/qr-code-dialog";
 import { DocumentUploadCard } from "@/components/document-upload-card";
 import { EmptyState } from "@/components/empty-state";
 import { HoneyBatchStorageCard } from "./honey-batch-storage-card";
+import { HoneyBatchContainerAllocationsCard } from "./honey-batch-container-allocations-card";
 import { Badge } from "@/components/ui/badge";
 import { Button } from "@/components/ui/button";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
@@ -83,6 +84,7 @@ export default function HoneyBatchDetailPage() {
             </CardContent>
           </Card>
           <HoneyBatchStorageCard honeyBatch={honeyBatch} />
+          <HoneyBatchContainerAllocationsCard honeyBatch={honeyBatch} />
         </div>
 
         <div className="flex flex-col gap-4 lg:col-span-2">