fix: swap SOC and grid-charging colors in battery chart (#379)

SOC is now green (#16a34a) and Grid→Battery is now blue (#3b82f6),
following up on #370.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: johanzander

frontend/src/components/BatteryLevelChart.tsx

@@ -31,9 +31,9 @@ export const BatteryLevelChart: React.FC<BatteryLevelChartProps> = ({ hourlyData
     background: isDarkMode ? '#1f2937' : '#ffffff',
     tooltip: isDarkMode ? '#374151' : '#ffffff',
     tooltipBorder: isDarkMode ? '#4b5563' : '#d1d5db',
-    soc: '#3b82f6',
+    soc: '#16a34a',
     solarCharging: '#fbbf24',
-    gridCharging: '#16a34a',
+    gridCharging: '#3b82f6',
     homeDischarging: '#f87171',
     gridDischarging: '#dc2626'
   };