add build step for flutter web, add persistent pagination in the traction list

lib/components/pages/new_traction.dart

@@ -84,6 +84,13 @@ class _NewTractionPageState extends State<NewTractionPage> {
       'traction_motors': TextEditingController(),
       'build_date': TextEditingController(),
     };
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (!mounted) return;
+      final data = context.read<DataService>();
+      if (data.locoClasses.isEmpty) {
+        data.fetchClassList();
+      }
+    });
   }
 
   @override
@@ -254,6 +261,10 @@ class _NewTractionPageState extends State<NewTractionPage> {
   @override
   Widget build(BuildContext context) {
     final isActive = _statusIsActive;
+    final data = context.watch<DataService>();
+    final classOptions = [...data.locoClasses]..sort(
+        (a, b) => a.toLowerCase().compareTo(b.toLowerCase()),
+      );
     final size = MediaQuery.of(context).size;
     final isNarrow = size.width < 720;
     final fieldWidth = isNarrow ? double.infinity : 340.0;
@@ -269,6 +280,89 @@ class _NewTractionPageState extends State<NewTractionPage> {
       double? widthOverride,
       String? Function(String?)? validator,
     }) {
+      // Special autocomplete for class field using existing loco classes.
+      if (key == 'class' && classOptions.isNotEmpty) {
+        return SizedBox(
+          width: widthOverride ?? fieldWidth,
+          child: Autocomplete<String>(
+            optionsBuilder: (TextEditingValue value) {
+              final query = value.text.trim().toLowerCase();
+              if (query.isEmpty) return classOptions;
+              return classOptions.where(
+                (c) => c.toLowerCase().contains(query),
+              );
+            },
+            onSelected: (selection) {
+              _controllers[key]?.text = selection;
+              _formKey.currentState?.validate();
+            },
+            fieldViewBuilder:
+                (context, textEditingController, focusNode, onFieldSubmitted) {
+              if (textEditingController.text != _controllers[key]?.text) {
+                WidgetsBinding.instance.addPostFrameCallback((_) {
+                  if (!mounted) return;
+                  if (textEditingController.text != _controllers[key]?.text) {
+                    textEditingController.value =
+                        _controllers[key]?.value ?? textEditingController.value;
+                  }
+                });
+              }
+              return TextFormField(
+                controller: textEditingController,
+                focusNode: focusNode,
+                decoration: InputDecoration(
+                  labelText: required ? '$label *' : label,
+                  helperText: helper,
+                  suffixText: suffixText,
+                  border: const OutlineInputBorder(),
+                ),
+                keyboardType: keyboardType,
+                maxLines: maxLines,
+                validator: (val) {
+                  if (required && (val == null || val.trim().isEmpty)) {
+                    return 'Required';
+                  }
+                  return validator?.call(val);
+                },
+                onChanged: (_) {
+                  _controllers[key]?.text = textEditingController.text;
+                  _formKey.currentState?.validate();
+                },
+                onFieldSubmitted: (_) => onFieldSubmitted(),
+              );
+            },
+            optionsViewBuilder: (context, onSelected, options) {
+              final opts = options.toList();
+              if (opts.isEmpty) return const SizedBox.shrink();
+              return Align(
+                alignment: Alignment.topLeft,
+                child: Material(
+                  elevation: 4,
+                  child: ConstrainedBox(
+                    constraints: BoxConstraints(
+                      maxHeight: 280,
+                      maxWidth: widthOverride ?? fieldWidth,
+                    ),
+                    child: ListView.builder(
+                      padding: EdgeInsets.zero,
+                      itemCount: opts.length,
+                      itemBuilder: (context, index) {
+                        final option = opts[index];
+                        return ListTile(
+                          dense: true,
+                          title: Text(option),
+                          onTap: () => onSelected(option),
+                        );
+                      },
+                    ),
+                  ),
+                ),
+              );
+            },
+          ),
+        );
+      }
+
       return SizedBox(
         width: widthOverride ?? fieldWidth,
         child: TextFormField(