feat: enhance product picker and improve error handling in inventory screen

flutter/lib/features/inventory/presentation/create_inventory_screen.dart

@@ -57,16 +57,26 @@ class _CreateInventoryScreenState
       final token = await ref.read(authStateProvider.future);
       final api = ref.read(apiClientProvider);
       final data = await api.getJson(ProductApiPaths.list, token: token);
+      final list = data is List<dynamic>
+          ? data
+          : (data is Map<String, dynamic> && data['items'] is List<dynamic>)
+              ? data['items'] as List<dynamic>
+              : const <dynamic>[];
       if (mounted) {
         setState(() {
-          _products = (data as List<dynamic>)
+          _products = list
               .map((e) => e as Map<String, dynamic>)
               .toList();
           _loadingProducts = false;
         });
       }
-    } catch (_) {
+    } catch (e) {
       if (mounted) setState(() => _loadingProducts = false);
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text(mapErrorToUserMessage(e, context))),
+        );
+      }
     }
   }
 
@@ -147,7 +157,7 @@ class _CreateInventoryScreenState
     final productOptions = sortedProducts
         .map(
           (p) => (
-            id: p['id'] as int,
+            id: (p['id'] as num).toInt(),
             name: (p['canonicalName'] ?? p['name'] ?? '').toString(),
           ),
         )