Added configurable shift types and holiday settings

lib/services/holidays_service.dart

@@ -0,0 +1,51 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+
+import '../models/rotation_config.dart';
+
+/// Provides holiday lookup via Nager.Date.
+class HolidaysService {
+  /// Fetches Philippine public holidays for [year].
+  ///
+  /// Returns a list of [Holiday] instances.
+  static Future<List<Holiday>> fetchPhilippinesHolidays(int year) async {
+    final uri = Uri.https('date.nager.at', '/api/v3/PublicHolidays/$year/PH');
+    final response = await http.get(uri);
+    if (response.statusCode != 200) {
+      throw Exception('Failed to fetch holidays: ${response.statusCode}');
+    }
+
+    final decoded = jsonDecode(response.body);
+    if (decoded is! List) {
+      throw Exception('Unexpected holiday response format');
+    }
+
+    return decoded
+        .whereType<Map<String, dynamic>>()
+        .map((item) {
+          final dateString = item['date'] as String?;
+          final name =
+              item['localName'] as String? ??
+              item['name'] as String? ??
+              'Holiday';
+
+          if (dateString == null) {
+            return null;
+          }
+
+          final parsed = DateTime.tryParse(dateString);
+          if (parsed == null) {
+            return null;
+          }
+
+          return Holiday(
+            date: DateTime(parsed.year, parsed.month, parsed.day),
+            name: name,
+            source: 'nager',
+          );
+        })
+        .whereType<Holiday>()
+        .toList();
+  }
+}