feat(i18n): 完成全量 UI 文本国际化，替换所有硬编码中文为 AppLocalizations 调用

- core/localization: 新增约 60 个翻译键（含参数化方法），中英双语覆盖
- shared/widgets: CommonDialog 默认参数国际化
- features/home: 完成页操作步骤指引、状态栏串口连接状态、程序列表状态标签
- features/programs: 表头状态列、表单验证提示、导入/模板操作反馈、删除确认（参数化）
- features/program_detail: 步骤列表/表单标题、删除确认、速度档位显示（参数化）
- features/device: run_state_provider 错误消息改为错误码
- features/settings: 升级页、密码面板、语言面板、U盘导入面板、串口配置面板全部替换

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/features/program_detail/widgets/step_form.dart

@@ -72,7 +72,7 @@ class _StepFormState extends State<StepForm> {
           children: [
             // 标题
             Text(
-              widget.isNew ? '添加步骤' : '编辑步骤',
+              widget.isNew ? (l10n?.addStep ?? '添加步骤') : (l10n?.editStep ?? '编辑步骤'),
               style: TextStyle(
                 color: AppTheme.textPrimary,
                 fontSize: 18,
@@ -86,12 +86,12 @@ class _StepFormState extends State<StepForm> {
               controller: _nameController,
               decoration: InputDecoration(
                 labelText: l10n?.stepName ?? '步骤名称',
-                hintText: '例如: 混合、吸磁、吹气',
+                hintText: l10n?.hintStepName ?? '例如: 混合、吸磁、吹气',
                 border: OutlineInputBorder(borderRadius: BorderRadius.circular(8)),
               ),
               validator: (value) {
                 if (value == null || value.trim().isEmpty) {
-                  return '请输入步骤名称';
+                  return l10n?.enterStepName ?? '请输入步骤名称';
                 }
                 return null;
               },
@@ -180,7 +180,7 @@ class _StepFormState extends State<StepForm> {
               crossAxisAlignment: CrossAxisAlignment.start,
               children: [
                 Text(
-                  '${l10n?.speed ?? '速度'}: $_speed 档',
+                  '${l10n?.speed ?? '速度'}: ${l10n?.speedLevelValue(_speed) ?? '$_speed 档'}',
                   style: TextStyle(color: AppTheme.textPrimary),
                 ),
                 Slider(

lib/features/program_detail/widgets/step_list.dart

@@ -53,7 +53,7 @@ class _StepListState extends State<StepList> {
                 Icon(Icons.list, color: AppTheme.primaryColor, size: 20),
                 const SizedBox(width: 12),
                 Text(
-                  '步骤列表',
+                  l10n?.stepList ?? '步骤列表',
                   style: TextStyle(
                     color: AppTheme.primaryColor,
                     fontWeight: FontWeight.w600,
@@ -61,7 +61,7 @@ class _StepListState extends State<StepList> {
                 ),
                 const Spacer(),
                 Text(
-                  '${widget.steps.length} 步',
+                  l10n?.stepsCountLabel(widget.steps.length) ?? '${widget.steps.length} 步',
                   style: TextStyle(
                     color: AppTheme.textSecondary,
                     fontSize: 12,
@@ -114,7 +114,7 @@ class _StepListState extends State<StepList> {
                       children: [
                         Icon(Icons.add_circle_outline, size: 48, color: AppTheme.idleColor),
                         const SizedBox(height: 12),
-                        Text('暂无步骤', style: TextStyle(color: AppTheme.textSecondary)),
+                        Text(l10n?.noSteps ?? '暂无步骤', style: TextStyle(color: AppTheme.textSecondary)),
                       ],
                     ),
                   )
@@ -149,7 +149,7 @@ class _StepListState extends State<StepList> {
               children: [
                 // 添加按钮
                 CommonButton(
-                  text: '添加',
+                  text: l10n?.add ?? '添加',
                   icon: Icons.add,
                   type: ButtonType.primary,
                   onPressed: widget.onAddStep,
@@ -158,7 +158,7 @@ class _StepListState extends State<StepList> {
                 // 删除按钮
                 if (_selectedIds.isNotEmpty)
                   CommonButton(
-                    text: '删除',
+                    text: l10n?.delete ?? '删除',
                     icon: Icons.delete,
                     type: ButtonType.danger,
                     onPressed: () => _showDeleteConfirmDialog(context),
@@ -241,8 +241,8 @@ class _StepListState extends State<StepList> {
         title: Text(l10n?.confirm ?? '确认'),
         content: Text(
           _selectedIds.length == 1
-              ? '确定要删除此步骤吗？'
-              : '确定要删除选中的 ${_selectedIds.length} 个步骤吗？',
+              ? l10n?.deleteStepConfirmSingle ?? '确定要删除此步骤吗？'
+              : l10n?.deleteStepConfirmMultiple(_selectedIds.length) ?? '确定要删除选中的 ${_selectedIds.length} 个步骤吗？',
         ),
         actions: [
           TextButton(