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/src/honey-batches/honey-batches.controller.ts

@@ -1,10 +1,12 @@
 import {
   Body,
   Controller,
+  Delete,
   Get,
   Param,
   Patch,
   Post,
+  Put,
   Query,
 } from '@nestjs/common';
 import { ApiBearerAuth, ApiTags } from '@nestjs/swagger';
@@ -16,6 +18,7 @@ import { CreateHoneyBatchDto } from './dto/create-honey-batch.dto';
 import { UpdateHoneyBatchDto } from './dto/update-honey-batch.dto';
 import { CreateHoneyMeasurementDto } from './dto/create-honey-measurement.dto';
 import { RelocateHoneyBatchDto } from './dto/relocate-honey-batch.dto';
+import { SetHoneyBatchContainerAllocationDto } from './dto/set-honey-batch-container-allocation.dto';
 import { HoneyBatchesService } from './honey-batches.service';
 
 @ApiTags('honey-batches')
@@ -48,6 +51,42 @@ export class HoneyBatchesController {
     return this.honeyBatchesService.findRelocations(id);
   }
 
+  @RequirePermission('honey-batches:read')
+  @Get(':id/containers')
+  listContainerAllocations(@Param('id') id: string) {
+    return this.honeyBatchesService.listContainerAllocations(id);
+  }
+
+  @RequirePermission('honey-batches:relocate')
+  @Put(':id/containers/:containerId')
+  setContainerAllocation(
+    @Param('id') id: string,
+    @Param('containerId') containerId: string,
+    @Body() dto: SetHoneyBatchContainerAllocationDto,
+    @CurrentUser() actor: AuthenticatedUser,
+  ) {
+    return this.honeyBatchesService.setContainerAllocation(
+      id,
+      containerId,
+      dto,
+      actor.id,
+    );
+  }
+
+  @RequirePermission('honey-batches:relocate')
+  @Delete(':id/containers/:containerId')
+  removeContainerAllocation(
+    @Param('id') id: string,
+    @Param('containerId') containerId: string,
+    @CurrentUser() actor: AuthenticatedUser,
+  ) {
+    return this.honeyBatchesService.removeContainerAllocation(
+      id,
+      containerId,
+      actor.id,
+    );
+  }
+
   @RequirePermission('honey-batches:relocate')
   @Post(':id/relocate')
   relocate(