fix: use primary color for all summary card icons (refs #2)

All summary cards now use primary.main for consistent branding

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

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

frontend/src/features/dashboard/components/SummaryCards.tsx

@@ -27,14 +27,14 @@ export const SummaryCards: React.FC<SummaryCardsProps> = ({ summary }) => {
       value: summary.upcomingMaintenanceCount,
       subtitle: 'Next 30 days',
       icon: BuildRoundedIcon,
-      color: 'warning.main',
+      color: 'primary.main',
     },
     {
       title: 'Recent Fuel Logs',
       value: summary.recentFuelLogsCount,
       subtitle: 'Last 7 days',
       icon: LocalGasStationRoundedIcon,
-      color: 'success.main',
+      color: 'primary.main',
     },
   ];