feat(programs): Excel 模板下载 + .xlsx 解析导入

- 新增 excel 4.0.6 / path_provider 2.1.5 依赖
- ExcelTemplateService：生成 Programs + Steps 双表模板（保存到应用文档目录）
- ExcelImportService：解析 .xlsx 并写入数据库，跳过已存在 code、按 program_code 关联步骤
- programs_page 顶部新增「下载模板」按钮，导入按钮改用 Excel 解析
- 移除被取代的 program_import_service.dart
- AppLocalizations 新增 downloadTemplate 键
- 验证：flutter analyze 无新增 issue；flutter build apk --debug 通过

lib/features/programs/services/excel_template_service.dart

@@ -0,0 +1,134 @@
+import 'dart:io';
+
+import 'package:excel/excel.dart';
+import 'package:path_provider/path_provider.dart';
+
+/// Excel 模板服务
+///
+/// 生成 .xlsx 模板用于程序/步骤批量导入。
+/// 模板包含两张表：
+///   - Programs：程序基础信息
+///   - Steps：步骤参数（通过 program_code 与 Programs 关联）
+class ExcelTemplateService {
+  static final ExcelTemplateService instance = ExcelTemplateService._internal();
+
+  ExcelTemplateService._internal();
+
+  /// 工作表名称
+  static const String sheetPrograms = 'Programs';
+  static const String sheetSteps = 'Steps';
+
+  /// 生成模板并保存到应用文档目录，返回文件对象
+  Future<File> generateTemplate() async {
+    final excel = Excel.createExcel();
+    final bytes = _buildTemplateBytes(excel);
+    final dir = await getApplicationDocumentsDirectory();
+    final file = File('${dir.path}/program_template.xlsx');
+    await file.writeAsBytes(bytes, flush: true);
+    return file;
+  }
+
+  /// 构建模板字节流（可在测试中直接调用）
+  List<int> _buildTemplateBytes(Excel excel) {
+    // 默认创建的第一个 sheet 重命名
+    final defaultSheet = excel.getDefaultSheet();
+    if (defaultSheet != null && defaultSheet != sheetPrograms) {
+      excel.rename(defaultSheet, sheetPrograms);
+    }
+
+    _writeProgramsSheet(excel);
+    _writeStepsSheet(excel);
+    return excel.encode()!;
+  }
+
+  void _writeProgramsSheet(Excel excel) {
+    final sheet = excel[sheetPrograms];
+    final headerStyle = CellStyle(
+      bold: true,
+      backgroundColorHex: ExcelColor.fromHexString('FFD9E1F2'),
+      horizontalAlign: HorizontalAlign.Center,
+    );
+
+    // 表头
+    final headers = ['code', 'name', 'temperature', 'airflowTime', 'status'];
+    sheet.appendRow(headers.map((h) => TextCellValue(h)).toList());
+    for (var i = 0; i < headers.length; i++) {
+      sheet
+          .cell(CellIndex.indexByColumnRow(columnIndex: i, rowIndex: 0))
+          .cellStyle = headerStyle;
+    }
+
+    // 示例行
+    final sample1 = ['P001', '示例程序-标准流程', 50, 60, 1];
+    final sample2 = ['P002', '示例程序-快速流程', 45, 30, 1];
+    sheet.appendRow(sample1.map((v) => TextCellValue(v.toString())).toList());
+    sheet.appendRow(sample2.map((v) => TextCellValue(v.toString())).toList());
+
+    // 说明行（用前缀标记，避免被解析）
+    final note = '说明：code 必填且唯一；name 必填；temperature/airflowTime 整数；status:1启用 0停用';
+    sheet.appendRow([TextCellValue(note)]);
+
+    // 列宽
+    sheet.setColumnWidth(0, 14);
+    sheet.setColumnWidth(1, 26);
+    sheet.setColumnWidth(2, 14);
+    sheet.setColumnWidth(3, 14);
+    sheet.setColumnWidth(4, 10);
+  }
+
+  void _writeStepsSheet(Excel excel) {
+    final sheet = excel[sheetSteps];
+    final headerStyle = CellStyle(
+      bold: true,
+      backgroundColorHex: ExcelColor.fromHexString('FFD9E1F2'),
+      horizontalAlign: HorizontalAlign.Center,
+    );
+
+    final headers = [
+      'program_code',
+      'step_no',
+      'position',
+      'name',
+      'mixTime',
+      'magnetTime',
+      'volume',
+      'blowTime',
+      'speed',
+    ];
+    sheet.appendRow(headers.map((h) => TextCellValue(h)).toList());
+    for (var i = 0; i < headers.length; i++) {
+      sheet
+          .cell(CellIndex.indexByColumnRow(columnIndex: i, rowIndex: 0))
+          .cellStyle = headerStyle;
+    }
+
+    // 示例行：P001 / P002 各两步
+    final samples = <List<Object>>[
+      ['P001', 1, 'A1', '加样', 30, 0, 500, 0, 5],
+      ['P001', 2, 'A2', '混合', 60, 10, 300, 30, 5],
+      ['P002', 1, 'B1', '混合', 20, 5, 400, 0, 4],
+    ];
+    for (final row in samples) {
+      sheet.appendRow(row.map((v) {
+        if (v is num) return IntCellValue(v.toInt());
+        return TextCellValue(v.toString());
+      }).toList());
+    }
+
+    // 说明行
+    final note =
+        '说明：program_code 对应 Programs.code；step_no 整数从 1 开始；position 形如 A1/B2；mixTime/magnetTime/volume/blowTime 单位秒或微升；speed 1-10';
+    sheet.appendRow([TextCellValue(note)]);
+
+    // 列宽
+    sheet.setColumnWidth(0, 14);
+    sheet.setColumnWidth(1, 10);
+    sheet.setColumnWidth(2, 12);
+    sheet.setColumnWidth(3, 14);
+    sheet.setColumnWidth(4, 10);
+    sheet.setColumnWidth(5, 12);
+    sheet.setColumnWidth(6, 10);
+    sheet.setColumnWidth(7, 10);
+    sheet.setColumnWidth(8, 8);
+  }
+}