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/apiaries/apiaries.service.ts

@@ -86,7 +86,7 @@ export class ApiariesService {
     });
     if (activeColonyCount > 0) {
       throw new ConflictException(
-        `Apiary ${id} still has ${activeColonyCount} active colonies - move or dissolve them first`,
+        `Der Bienenstand hat noch ${activeColonyCount} aktive(s) Volk/Völker - zuerst verlegen oder auflösen`,
       );
     }
     const apiary = await this.prisma.apiary.update({