feat: environment widgets layout redesign with always-visible widgets

- Desktop: 4-in-a-row layout (30/20/20/30 distribution)
- Tablet: 2x2 grid layout
- Mobile: Stacked vertically
- All widgets show "No data available" state instead of being hidden
- Sun position calculates from clock, defaults to 6am/6pm
- Environment refresh changed from 5min to 1 hour

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/shared/widgets/sun_position_widget.dart

@@ -130,9 +130,13 @@ class SunPositionWidget extends StatelessWidget {
   }
 
   bool get _isDaytime {
-    if (sunTimes?.sunrise == null || sunTimes?.sunset == null) return true;
     final now = DateTime.now();
-    return now.isAfter(sunTimes!.sunrise!) && now.isBefore(sunTimes!.sunset!);
+    // Use actual sun times if available, otherwise default to 6am/6pm
+    final sunrise = sunTimes?.sunrise ??
+        DateTime(now.year, now.month, now.day, 6, 0);
+    final sunset = sunTimes?.sunset ??
+        DateTime(now.year, now.month, now.day, 18, 0);
+    return now.isAfter(sunrise) && now.isBefore(sunset);
   }
 
   String _formatTime(DateTime? time) {
@@ -370,14 +374,13 @@ class _SunArcPainter extends CustomPainter {
   }
 
   double _calculateSunPosition() {
-    if (sunTimes?.sunrise == null || sunTimes?.sunset == null) {
-      // Default to noon position
-      return 0.5;
-    }
-
     final now = DateTime.now();
-    final sunrise = sunTimes!.sunrise!;
-    final sunset = sunTimes!.sunset!;
+
+    // Use actual sun times if available, otherwise default to 6am/6pm (12-hour cycles)
+    final sunrise = sunTimes?.sunrise ??
+        DateTime(now.year, now.month, now.day, 6, 0);
+    final sunset = sunTimes?.sunset ??
+        DateTime(now.year, now.month, now.day, 18, 0);
 
     // Before sunrise
     if (now.isBefore(sunrise)) {