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/queens/queens.service.ts

@@ -157,7 +157,7 @@ export class QueensService {
     const queen = await this.findById(id);
     if (QUEEN_NO_LONGER_AVAILABLE_STATUSES.includes(queen.status)) {
       throw new ConflictException(
-        `Queen ${id} is not available for assignment (status: ${queen.status}) - correct her status first if this was a mistake`,
+        'Die Königin ist nicht mehr verfügbar für eine Zuweisung - korrigiere zuerst ihren Status, falls dies ein Versehen war',
       );
     }
     const colony = await this.prisma.colony.findUnique({