fix: sleep import groups segments by gap instead of date boundary

Problem: Segments crossing midnight were split into different nights
- 22:30-23:15 (21.03) → assigned to 21.03
- 00:30-02:45 (22.03) → assigned to 22.03
But both belong to the same night (21/22.03)!

Solution: Gap-based grouping
- Sort segments chronologically
- Group segments with gap < 2 hours
- Night date = wake_time.date() (last segment's end date)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/routers/sleep.py

@@ -484,13 +484,20 @@ async def import_apple_health_sleep(
             'phase': phase_en
         })
 
-    # Group by night (wake date)
-    nights = {}
-    for seg in segments:
-        wake_date = seg['end'].date()  # Date of waking up
+    # Sort segments chronologically
+    segments.sort(key=lambda s: s['start'])
 
-        if wake_date not in nights:
-            nights[wake_date] = {
+    # Group segments into nights (gap-based)
+    # If gap between segments > 2 hours → new night
+    nights = []
+    current_night = None
+
+    for seg in segments:
+        # Start new night if:
+        # 1. First segment
+        # 2. Gap > 2 hours since last segment
+        if current_night is None or (seg['start'] - current_night['wake_time']).total_seconds() > 7200:
+            current_night = {
                 'bedtime': seg['start'],
                 'wake_time': seg['end'],
                 'segments': [],
@@ -499,21 +506,28 @@ async def import_apple_health_sleep(
                 'light_minutes': 0,
                 'awake_minutes': 0
             }
+            nights.append(current_night)
 
-        night = nights[wake_date]
-        night['segments'].append(seg)
-        night['wake_time'] = max(night['wake_time'], seg['end'])  # Latest wake time
-        night['bedtime'] = min(night['bedtime'], seg['start'])    # Earliest bed time
+        # Add segment to current night
+        current_night['segments'].append(seg)
+        current_night['wake_time'] = max(current_night['wake_time'], seg['end'])
+        current_night['bedtime'] = min(current_night['bedtime'], seg['start'])
 
         # Sum phases
         if seg['phase'] == 'deep':
-            night['deep_minutes'] += seg['duration_min']
+            current_night['deep_minutes'] += seg['duration_min']
         elif seg['phase'] == 'rem':
-            night['rem_minutes'] += seg['duration_min']
+            current_night['rem_minutes'] += seg['duration_min']
         elif seg['phase'] == 'light':
-            night['light_minutes'] += seg['duration_min']
+            current_night['light_minutes'] += seg['duration_min']
         elif seg['phase'] == 'awake':
-            night['awake_minutes'] += seg['duration_min']
+            current_night['awake_minutes'] += seg['duration_min']
+
+    # Convert nights list to dict with wake_date as key
+    nights_dict = {}
+    for night in nights:
+        wake_date = night['wake_time'].date()  # Date when you woke up
+        nights_dict[wake_date] = night
 
     # Insert nights
     imported = 0
@@ -522,7 +536,7 @@ async def import_apple_health_sleep(
     with get_db() as conn:
         cur = get_cursor(conn)
 
-        for date, night in nights.items():
+        for date, night in nights_dict.items():
             # Calculate total duration (sum of all phases)
             duration_minutes = (
                 night['deep_minutes'] +
@@ -593,6 +607,6 @@ async def import_apple_health_sleep(
     return {
         "imported": imported,
         "skipped": skipped,
-        "total_nights": len(nights),
+        "total_nights": len(nights_dict),
         "message": f"{imported} Nächte importiert, {skipped} übersprungen (manuelle Einträge)"
     }