Initial project import and stabilization baseline

lib/core/hijri_date.dart

@@ -0,0 +1,74 @@
+class HijriDate {
+  final int year;
+  final int month;
+  final int day;
+
+  const HijriDate({
+    required this.year,
+    required this.month,
+    required this.day,
+  });
+}
+
+class HijriDateFormatter {
+  HijriDateFormatter._();
+
+  static const List<String> _monthNames = [
+    'Muharram',
+    'Safar',
+    'Rabiul Awal',
+    'Rabiul Akhir',
+    'Jumadil Awal',
+    'Jumadil Akhir',
+    'Rajab',
+    'Syaban',
+    'Ramadan',
+    'Syawal',
+    'Zulkaidah',
+    'Zulhijah',
+  ];
+
+  static String format(DateTime date) {
+    final hijri = fromGregorian(date);
+    final monthName = _monthNames[hijri.month - 1];
+    return '${hijri.day} $monthName ${hijri.year} H';
+  }
+
+  // Tabular Islamic calendar conversion. This is deterministic and avoids
+  // adding a new dependency just to replace the hardcoded placeholder dates.
+  static HijriDate fromGregorian(DateTime date) {
+    final jd = _gregorianToJulianDay(date.year, date.month, date.day);
+
+    var l = jd - 1948440 + 10632;
+    final n = ((l - 1) ~/ 10631);
+    l = l - 10631 * n + 354;
+
+    final j = (((10985 - l) ~/ 5316) * ((50 * l) ~/ 17719)) +
+        ((l ~/ 5670) * ((43 * l) ~/ 15238));
+
+    l = l -
+        (((30 - j) ~/ 15) * ((17719 * j) ~/ 50)) -
+        ((j ~/ 16) * ((15238 * j) ~/ 43)) +
+        29;
+
+    final month = (24 * l) ~/ 709;
+    final day = l - ((709 * month) ~/ 24);
+    final year = 30 * n + j - 30;
+
+    return HijriDate(year: year, month: month, day: day);
+  }
+
+  static int _gregorianToJulianDay(int year, int month, int day) {
+    final a = (14 - month) ~/ 12;
+    final y = year + 4800 - a;
+    final m = month + 12 * a - 3;
+
+    return day +
+        ((153 * m + 2) ~/ 5) +
+        365 * y +
+        (y ~/ 4) -
+        (y ~/ 100) +
+        (y ~/ 400) -
+        32045;
+  }
+}