feat(sun-position): redesign arc to touch horizon at endpoints

- Arc geometry now uses chord-radius calculation for proper horizon intersection
- Sunrise/sunset icons integrated at horizon endpoints (removed duplicate labels)
- Daylight duration centered below arc
- Increased all environment card heights 20% (140px → 170px) for better arc visibility
- Visual balance: sunrise/sunset raised 10px, daylight at bottom

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

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

lib/shared/widgets/forecast_widget.dart

@@ -48,28 +48,30 @@ class ForecastWidget extends StatelessWidget {
                   ),
                 ],
               ),
-              // Match height of populated card content area
-              const SizedBox(height: 120),
-              Center(
-                child: Column(
-                  mainAxisSize: MainAxisSize.min,
-                  children: [
-                    Icon(
-                      Icons.event_busy_outlined,
-                      size: 32,
-                      color: colorScheme.outline,
-                    ),
-                    const SizedBox(height: 8),
-                    Text(
-                      'No data available',
-                      style: Theme.of(context).textTheme.bodyMedium?.copyWith(
-                            color: colorScheme.outline,
-                          ),
-                    ),
-                  ],
+              const SizedBox(height: 8),
+              // Match sun position card height (170px content area)
+              SizedBox(
+                height: 170,
+                child: Center(
+                  child: Column(
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      Icon(
+                        Icons.event_busy_outlined,
+                        size: 32,
+                        color: colorScheme.outline,
+                      ),
+                      const SizedBox(height: 8),
+                      Text(
+                        'No data available',
+                        style: Theme.of(context).textTheme.bodyMedium?.copyWith(
+                              color: colorScheme.outline,
+                            ),
+                      ),
+                    ],
+                  ),
                 ),
               ),
-              const SizedBox(height: 40),
             ],
           ),
         ),