ui: change calibration icon to Icons.tune

lib/features/sensors/calibration_sheet.dart

@@ -180,7 +180,7 @@ class _IntroPage extends StatelessWidget {
             ),
             const SizedBox(height: 32),
             Icon(
-              Icons.radar,
+              Icons.tune,
               size: 56,
               color: theme.colorScheme.primary,
             ),

lib/features/sensors/sensor_detail_sheet.dart

@@ -234,7 +234,7 @@ class _SheetBody extends StatelessWidget {
             ),
             const SizedBox(height: 12),
             OutlinedButton.icon(
-              icon: const Icon(Icons.radar),
+              icon: const Icon(Icons.tune),
               label: const Text('Calibrate'),
               onPressed: onCalibrate,
             ),