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-Frontend/src/app/(app)/apiaries/[id]/apiary-edit-card.tsx

@@ -5,6 +5,7 @@ import { MapPin } from "lucide-react";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { toast } from "sonner";
 import { deactivateApiary, reactivateApiary, updateApiary } from "@/lib/apiaries/api";
+import { ApiError } from "@/lib/auth/api-client";
 import { Apiary } from "@/lib/apiaries/types";
 import { Button } from "@/components/ui/button";
 import { Badge } from "@/components/ui/badge";
@@ -54,7 +55,10 @@ export function ApiaryEditCard({ apiary }: { apiary: Apiary }) {
         description: "Er kann jederzeit über „Reaktivieren“ wiederhergestellt werden.",
       });
     },
-    onError: () => toast.error("Bienenstand konnte nicht deaktiviert werden"),
+    onError: (error) =>
+      toast.error(
+        error instanceof ApiError ? error.message : "Bienenstand konnte nicht deaktiviert werden",
+      ),
   });
 
   const reactivateMutation = useMutation({

ApiCore-Frontend/src/app/(app)/colonies/[id]/colony-actions.tsx

@@ -3,6 +3,7 @@
 import { FormEvent, useState } from "react";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { toast } from "sonner";
+import { ApiError } from "@/lib/auth/api-client";
 import {
   dissolveColony,
   mergeColony,
@@ -35,6 +36,10 @@ import {
   SelectValue,
 } from "@/components/ui/select";
 
+function errorMessage(error: unknown, fallback: string): string {
+  return error instanceof ApiError ? error.message : fallback;
+}
+
 function invalidateColony(
   queryClient: ReturnType<typeof useQueryClient>,
   colonyId: string,
@@ -59,6 +64,8 @@ function MoveDialog({ colony }: { colony: Colony }) {
       invalidateColony(queryClient, colony.id);
       setOpen(false);
     },
+    onError: (error) =>
+      toast.error(errorMessage(error, "Volk konnte nicht umgesetzt werden")),
   });
 
   return (
@@ -122,6 +129,8 @@ function SplitDialog({ colony }: { colony: Colony }) {
       void queryClient.invalidateQueries({ queryKey: ["colonies"] });
       setOpen(false);
     },
+    onError: (error) =>
+      toast.error(errorMessage(error, "Ableger konnte nicht angelegt werden")),
   });
 
   return (
@@ -196,6 +205,8 @@ function AssignQueenDialog({ colony }: { colony: Colony }) {
       void queryClient.invalidateQueries({ queryKey: ["queens"] });
       setOpen(false);
     },
+    onError: (error) =>
+      toast.error(errorMessage(error, "Königin konnte nicht zugewiesen werden")),
   });
 
   return (
@@ -259,6 +270,8 @@ function MergeDialog({ colony }: { colony: Colony }) {
       void queryClient.invalidateQueries({ queryKey: ["colonies"] });
       setOpen(false);
     },
+    onError: (error) =>
+      toast.error(errorMessage(error, "Völker konnten nicht vereinigt werden")),
   });
 
   return (

ApiCore-Frontend/src/app/(app)/queens/[id]/assign-colony-dialog.tsx

@@ -4,6 +4,7 @@ import { FormEvent, useState } from "react";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { toast } from "sonner";
 import { assignQueenColony } from "@/lib/queens/api";
+import { ApiError } from "@/lib/auth/api-client";
 import { QUEEN_UNAVAILABLE_STATUSES } from "@/lib/queens/labels";
 import { QueenStatus } from "@/lib/queens/types";
 import { fetchColonies } from "@/lib/colonies/api";
@@ -45,7 +46,10 @@ export function AssignColonyDialog({
       void queryClient.invalidateQueries({ queryKey: ["queens", queenId, "history"] });
       setOpen(false);
     },
-    onError: () => toast.error("Volk konnte nicht zugewiesen werden"),
+    onError: (error) =>
+      toast.error(
+        error instanceof ApiError ? error.message : "Volk konnte nicht zugewiesen werden",
+      ),
   });
 
   return (

ApiCore-Frontend/src/app/(app)/storage/record-movement-dialog.tsx

@@ -3,6 +3,7 @@
 import { FormEvent, useState } from "react";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { addStockMovement } from "@/lib/storage/api";
+import { ApiError } from "@/lib/auth/api-client";
 import { StockMovementType } from "@/lib/storage/types";
 import { STOCK_MOVEMENT_TYPES, STOCK_MOVEMENT_TYPE_LABELS } from "@/lib/storage/labels";
 import { Button } from "@/components/ui/button";
@@ -40,8 +41,10 @@ export function RecordMovementDialog({ stockItemId }: { stockItemId: string }) {
       setQuantity("");
       setError(null);
     },
-    onError: () => {
-      setError("Bewegung konnte nicht gespeichert werden.");
+    onError: (error) => {
+      setError(
+        error instanceof ApiError ? error.message : "Bewegung konnte nicht gespeichert werden.",
+      );
     },
   });