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/storage/storage.service.ts

@@ -134,7 +134,7 @@ export class StorageService {
     // that is the only way to correct a stock count downward.
     if (dto.type !== 'ADJUSTMENT' && dto.quantity <= 0) {
       throw new BadRequestException(
-        'quantity must be positive for IN/OUT movements - the direction is determined by "type"',
+        'Menge muss bei Eingang/Ausgang positiv sein - die Richtung wird durch den Bewegungstyp bestimmt',
       );
     }
     const delta =