feat(sun-position): add proportional arc visualization with 10-min updates

- Arc angle now proportional to day/night duration (day = daylight/24 × 360°)
- Horizon points represent sunrise/sunset times
- Day arc with sun icon and yellow/orange gradient
- Night arc with moon icon and blue/indigo gradient
- Position updates every 10 minutes aligned to clock (0/10/20/30/40/50)
- Default to 07:00-17:00 when API data unavailable (asymmetric for visual effect)
- All environment cards maintain consistent height in "no data" state

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

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

lib/shared/widgets/weather_widget.dart

@@ -212,9 +212,11 @@ class WeatherWidget extends StatelessWidget {
                 ),
               ],
             ),
-            const SizedBox(height: 24),
+            // Match height of populated card content area
+            const SizedBox(height: 120),
             Center(
               child: Column(
+                mainAxisSize: MainAxisSize.min,
                 children: [
                   Icon(
                     Icons.cloud_off_outlined,
@@ -231,7 +233,7 @@ class WeatherWidget extends StatelessWidget {
                 ],
               ),
             ),
-            const SizedBox(height: 16),
+            const SizedBox(height: 40),
           ],
         ),
       ),