feat(web): show retry prompt when a category fails to load from source

When getCategoryWithParts reports loadError (the PL24 catalog fetch failed
rather than the category being genuinely empty), the leaf view now renders a
"Katalog şu an yüklenemedi — tekrar dene" alert with a retry button instead of
the misleading "Bu kategori için parça bulunamadı" empty state. Genuine empty
leaves are unaffected.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/routes/dashboard/vehicles_/$id/categories_/$categoryId.tsx

@@ -238,19 +238,44 @@ function VehicleCategoryPage() {
           <CategoryColumns categories={data.children} vehicleId={id} />
         ))}
 
-      {/* Leaf category — show schema viewer */}
-      {data && !hasChildren && (
-        <Suspense fallback={<SchemaViewerFallback />}>
-          <SchemaViewer
-            schemaPic={data.schemaPics?.[0] ?? null}
-            hotspots={data.hotspots ?? []}
-            parts={data.parts ?? []}
-            isLoading={isLoading}
-            vehicleId={id}
-            categoryId={categoryId}
-          />
-        </Suspense>
-      )}
+      {/* Leaf category — schema viewer, or a retry prompt when the source
+          catalog fetch failed (vs a genuinely empty category). */}
+      {data &&
+        !hasChildren &&
+        (data.loadError ? (
+          <div
+            role="alert"
+            className="flex flex-col items-start gap-3 rounded-lg border border-destructive/40 bg-destructive/5 p-5 text-sm"
+          >
+            <div>
+              <p className="font-medium text-destructive">Katalog şu an yüklenemedi</p>
+              <p className="mt-1 text-muted-foreground">
+                Bu kategori tedarikçi katalogundan alınamadı. Lütfen birazdan tekrar deneyin.
+              </p>
+            </div>
+            <Button
+              type="button"
+              size="sm"
+              variant="outline"
+              onClick={() => refetch()}
+              disabled={isFetching}
+              data-faro-user-action-name="category-loaderror-retry"
+            >
+              {isFetching ? "Yükleniyor…" : "Tekrar dene"}
+            </Button>
+          </div>
+        ) : (
+          <Suspense fallback={<SchemaViewerFallback />}>
+            <SchemaViewer
+              schemaPic={data.schemaPics?.[0] ?? null}
+              hotspots={data.hotspots ?? []}
+              parts={data.parts ?? []}
+              isLoading={isLoading}
+              vehicleId={id}
+              categoryId={categoryId}
+            />
+          </Suspense>
+        ))}
     </div>
   );
 }