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-Backend/prisma/schema.prisma

@@ -708,9 +708,10 @@ model HoneyBatch {
   createdAt          DateTime          @default(now())
   updatedAt          DateTime          @updatedAt
 
-  measurements    HoneyMeasurement[]
-  bottlingBatches BottlingBatch[]
-  relocations     HoneyBatchRelocation[]
+  measurements        HoneyMeasurement[]
+  bottlingBatches     BottlingBatch[]
+  relocations         HoneyBatchRelocation[]
+  containerAllocations HoneyBatchContainerAllocation[]
 
   @@index([status])
   @@index([extractionId])
@@ -756,9 +757,10 @@ model StorageContainer {
   createdAt     DateTime               @default(now())
   updatedAt     DateTime               @updatedAt
 
-  honeyBatches    HoneyBatch[]
-  relocationsFrom HoneyBatchRelocation[] @relation("RelocationFrom")
-  relocationsTo   HoneyBatchRelocation[] @relation("RelocationTo")
+  honeyBatches        HoneyBatch[]
+  relocationsFrom     HoneyBatchRelocation[]          @relation("RelocationFrom")
+  relocationsTo       HoneyBatchRelocation[]           @relation("RelocationTo")
+  batchAllocations    HoneyBatchContainerAllocation[]
 
   @@index([status])
 }
@@ -781,6 +783,27 @@ model HoneyBatchRelocation {
   @@index([honeyBatchId, relocatedAt])
 }
 
+// Aufteilung einer Honigcharge auf mehrere Lagerbehälter (z.B. 125 kg auf 5
+// Eimer à 25 kg) - additiv zum obigen "primären" storageContainerId/
+// Umlagern-Fluss auf HoneyBatch, der weiterhin den einfachen Ein-Behälter-
+// Fall abdeckt; diese Tabelle bildet zusätzlich den Fall ab, dass eine
+// Charge zu groß für einen einzelnen Behälter ist. @@unique macht das
+// Zuweisen einer Menge zu einem Behälter ein Upsert (erneutes Zuweisen
+// überschreibt die Menge, statt einen Duplikat-Eintrag anzulegen).
+model HoneyBatchContainerAllocation {
+  id                 String           @id @default(cuid())
+  honeyBatchId       String
+  honeyBatch         HoneyBatch       @relation(fields: [honeyBatchId], references: [id])
+  storageContainerId String
+  storageContainer   StorageContainer @relation(fields: [storageContainerId], references: [id])
+  amount             Float
+  createdAt          DateTime         @default(now())
+  updatedAt          DateTime         @updatedAt
+
+  @@unique([honeyBatchId, storageContainerId])
+  @@index([storageContainerId])
+}
+
 enum StockCategory {
   HONEY
   CONSUMABLE