Implement husband-wife connection dialogue and theme support for learn articles

lib/services/cycle_service.dart

@@ -175,6 +175,66 @@ class CycleService {
     );
   }
 
+  /// Calculates the cycle phase for a specific date (past or future)
+  static CyclePhase? getPhaseForDate(DateTime date, UserProfile? user) {
+    if (user == null || user.lastPeriodStartDate == null) return null;
+
+    final lastPeriodStart = user.lastPeriodStartDate!;
+    
+    // Normalize dates
+    final checkDate = DateTime(date.year, date.month, date.day);
+    final startCycle = DateTime(lastPeriodStart.year, lastPeriodStart.month, lastPeriodStart.day);
+
+    final daysDifference = checkDate.difference(startCycle).inDays;
+    
+    // If date is before the last known period, we can't reliably predict using this simple logic
+    // (though in reality we could project backwards, but let's stick to forward/current)
+    if (daysDifference < 0) return null;
+
+    final cycleLength = user.averageCycleLength;
+    final dayOfCycle = (daysDifference % cycleLength) + 1;
+
+    if (dayOfCycle <= user.averagePeriodLength) return CyclePhase.menstrual;
+    if (dayOfCycle <= 13) return CyclePhase.follicular;
+    if (dayOfCycle <= 16) return CyclePhase.ovulation;
+    return CyclePhase.luteal;
+  }
+
+  /// Predicts period days for the next [months] months
+  static List<DateTime> predictNextPeriodDays(UserProfile? user, {int months = 12}) {
+    if (user == null || user.lastPeriodStartDate == null) return [];
+
+    final predictedDays = <DateTime>[];
+    final lastPeriodStart = user.lastPeriodStartDate!;
+    final cycleLength = user.averageCycleLength;
+    final periodLength = user.averagePeriodLength;
+
+    // Start predicting from the NEXT cycle if the current one is finished, 
+    // or just project out from the last start date.
+    // We want to list all future period days.
+    
+    DateTime currentCycleStart = lastPeriodStart;
+    
+    // Project forward for roughly 'months' months
+    // A safe upper bound for loop is months * 30 days
+    final limitDate = DateTime.now().add(Duration(days: months * 30));
+
+    while (currentCycleStart.isBefore(limitDate)) {
+      // Add period days for this cycle
+      for (int i = 0; i < periodLength; i++) {
+        final periodDay = currentCycleStart.add(Duration(days: i));
+        if (periodDay.isAfter(DateTime.now())) {
+          predictedDays.add(periodDay);
+        }
+      }
+      
+      // Move to next cycle
+      currentCycleStart = currentCycleStart.add(Duration(days: cycleLength));
+    }
+    
+    return predictedDays;
+  }
+
   /// Format cycle day for display
   static String getDayOfCycleDisplay(int day) => 'Day $day';