feat(service): add foreground service for background message sync

Implement Android foreground service to keep app alive in background for real-time message sync:
- Add withForegroundService expo config plugin for notification channel setup
- Add BackgroundSyncManager with REALTIME, BATTERY_SAVER, and DISABLED modes
- Add ForegroundServiceModule for native Android foreground service binding
- Refactor backgroundService to integrate foreground service and expo-background-task

Also refactor auth and profile screens to use dynamic theme colors:
- Replace hardcoded THEME_COLORS with colors.primary.main, colors.background.paper, etc.
- Add useResolvedColorScheme for dynamic StatusBar styling
- Update NotificationSettingsScreen with sync mode selection UI

BREAKING CHANGE: Switched from expo-background-fetch to expo-background-task, minimum background sync interval changed from 900s to 15min in config

src/screens/auth/RegisterStep1Email.tsx

@@ -15,12 +15,6 @@ import { MaterialCommunityIcons } from '@expo/vector-icons';
 import { useAppColors, type AppColors } from '../../theme';
 import { RegisterStepProps } from './types';
 
-const THEME_COLORS = {
-  primary: '#FF6B35',
-  primaryLight: '#FF8C5A',
-  primaryDark: '#E55A2B',
-};
-
 export const RegisterStep1Email: React.FC<RegisterStepProps> = ({
   formData,
   updateFormData,
@@ -91,7 +85,7 @@ export const RegisterStep1Email: React.FC<RegisterStepProps> = ({
                 <MaterialCommunityIcons
                   name="check-circle"
                   size={20}
-                  color={THEME_COLORS.primary}
+                  color={colors.primary.main}
                   style={styles.checkIcon}
                 />
               )}
@@ -145,7 +139,7 @@ function createStyles(colors: AppColors) {
     inputWrapper: {
       flexDirection: 'row',
       alignItems: 'center',
-      backgroundColor: '#F5F5F7',
+      backgroundColor: colors.background.default,
       borderRadius: 14,
       paddingHorizontal: 18,
       height: 56,
@@ -173,7 +167,7 @@ function createStyles(colors: AppColors) {
     actionButton: {
       height: 56,
       borderRadius: 14,
-      backgroundColor: '#FF6B35',
+      backgroundColor: colors.primary.main,
       alignItems: 'center',
       justifyContent: 'center',
       marginTop: 8,
@@ -184,7 +178,7 @@ function createStyles(colors: AppColors) {
     actionButtonText: {
       fontSize: 17,
       fontWeight: '600',
-      color: '#FFFFFF',
+      color: colors.text.inverse,
     },
   });
 }