fix: surface specific business-rule error messages to beekeepers

Backend business-rule guards (inactive apiary blocking colony
create/move, active colonies blocking apiary deactivation, negative
quantity on IN/OUT stock movements, unavailable queen blocking colony
assignment, inactive colony blocking split/merge/move) threw English,
UUID-laden exception text that the frontend either discarded in favor
of a generic message or - in colony-actions.tsx's move/split/merge/
assign-queen dialogs - didn't handle at all, so the guard fired with
zero visible feedback. Translated the messages to plain German and
wired the affected mutations to display them, so a beekeeper sees the
actual reason a save was rejected instead of silence or "failed".

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

ApiCore-Backend/src/colonies/colonies.service.ts

@@ -46,7 +46,7 @@ export class ColoniesService {
   private assertActive(colony: Colony): void {
     if (colony.status !== 'ACTIVE') {
       throw new ConflictException(
-        `Colony ${colony.id} is not active (status: ${colony.status})`,
+        `Das Volk ist nicht aktiv (Status: ${colony.status})`,
       );
     }
   }
@@ -61,11 +61,11 @@ export class ColoniesService {
       where: { id: apiaryId },
     });
     if (!apiary) {
-      throw new NotFoundException(`Apiary ${apiaryId} not found`);
+      throw new NotFoundException('Bienenstand nicht gefunden');
     }
     if (apiary.status !== 'ACTIVE') {
       throw new ConflictException(
-        `Apiary ${apiaryId} is not active (status: ${apiary.status})`,
+        'Der Bienenstand ist nicht aktiv und kann daher keine Völker aufnehmen',
       );
     }
   }
@@ -190,7 +190,9 @@ export class ColoniesService {
           where: { id: mergedColonyId },
         });
         if (!merged) {
-          throw new NotFoundException(`Colony ${mergedColonyId} not found`);
+          throw new NotFoundException(
+            'Zu vereinigendes Volk wurde nicht gefunden',
+          );
         }
         this.assertActive(merged);
         // currentQueenId is unique across colonies - if it stayed set on