feat: add support for dynamic background and gradient colors in theme configuration

lib/screens/main_shell.dart

@@ -191,9 +191,9 @@ class _MainShellState extends State<MainShell> {
                 begin: Alignment.topCenter,
                 end: Alignment.bottomCenter,
                 colors: [
-                  colorScheme.surfaceContainerLowest,
-                  colorScheme.surface,
-                  const Color(0xFFF3EAD3), // Warm traditional restaurant sand/cream
+                  ThemeManager.instance.backgroundColor,
+                  ThemeManager.instance.backgroundColor,
+                  ThemeManager.instance.backgroundGradientColor,
                 ],
               ),
             ),

lib/services/odoo_service.dart

@@ -116,11 +116,15 @@ class OdooService {
           'brand_logo': (res['brand_logo'] as String?) ?? '',
           'primary_color': (res['primary_color'] as String?) ?? '#C62828',
           'secondary_color': (res['secondary_color'] as String?) ?? '#FF8F00',
+          'background_color': (res['background_color'] as String?) ?? '#FAF6EE',
+          'background_gradient_color': (res['background_gradient_color'] as String?) ?? '#F3EAD3',
         };
         // Save and apply new branding and theme colors dynamically
         await ThemeManager.instance.updateConfig(
           primaryHex: configMap['primary_color']!,
           secondaryHex: configMap['secondary_color']!,
+          backgroundHex: configMap['background_color']!,
+          backgroundGradientHex: configMap['background_gradient_color']!,
           brandLogoB64: configMap['brand_logo']!,
         );
         return configMap;

lib/services/theme_manager.dart

@@ -11,15 +11,20 @@ class ThemeManager extends ChangeNotifier {
 
   Color _primaryColor = AppTheme.primary;
   Color _secondaryColor = AppTheme.secondary;
+  Color _backgroundColor = AppTheme.surface;
+  Color _backgroundGradientColor = const Color(0xFFF3EAD3);
   String _brandLogo = '';
 
   Color get primaryColor => _primaryColor;
   Color get secondaryColor => _secondaryColor;
+  Color get backgroundColor => _backgroundColor;
+  Color get backgroundGradientColor => _backgroundGradientColor;
   String get brandLogo => _brandLogo;
 
   ThemeData get themeData => AppTheme.getTheme(
         primaryColor: _primaryColor,
         secondaryColor: _secondaryColor,
+        backgroundColor: _backgroundColor,
       );
 
   /// Initialize cached settings on app launch
@@ -27,6 +32,8 @@ class ThemeManager extends ChangeNotifier {
     final prefs = await SharedPreferences.getInstance();
     final primHex = prefs.getString('theme_primary_color');
     final secHex = prefs.getString('theme_secondary_color');
+    final bgHex = prefs.getString('theme_background_color');
+    final bgGradHex = prefs.getString('theme_background_gradient_color');
     _brandLogo = prefs.getString('theme_brand_logo') ?? '';
 
     if (primHex != null) {
@@ -35,21 +42,33 @@ class ThemeManager extends ChangeNotifier {
     if (secHex != null) {
       _secondaryColor = _parseHexColor(secHex) ?? AppTheme.secondary;
     }
+    if (bgHex != null) {
+      _backgroundColor = _parseHexColor(bgHex) ?? AppTheme.surface;
+    }
+    if (bgGradHex != null) {
+      _backgroundGradientColor = _parseHexColor(bgGradHex) ?? const Color(0xFFF3EAD3);
+    }
   }
 
   /// Update theme options and persist them to SharedPreferences
   Future<void> updateConfig({
     required String primaryHex,
     required String secondaryHex,
+    required String backgroundHex,
+    required String backgroundGradientHex,
     required String brandLogoB64,
   }) async {
     final prefs = await SharedPreferences.getInstance();
     await prefs.setString('theme_primary_color', primaryHex);
     await prefs.setString('theme_secondary_color', secondaryHex);
+    await prefs.setString('theme_background_color', backgroundHex);
+    await prefs.setString('theme_background_gradient_color', backgroundGradientHex);
     await prefs.setString('theme_brand_logo', brandLogoB64);
 
     _primaryColor = _parseHexColor(primaryHex) ?? AppTheme.primary;
     _secondaryColor = _parseHexColor(secondaryHex) ?? AppTheme.secondary;
+    _backgroundColor = _parseHexColor(backgroundHex) ?? AppTheme.surface;
+    _backgroundGradientColor = _parseHexColor(backgroundGradientHex) ?? const Color(0xFFF3EAD3);
     _brandLogo = brandLogoB64;
     notifyListeners();
   }

lib/theme/app_theme.dart

@@ -25,10 +25,11 @@ class AppTheme {
 
   static ThemeData get lightTheme => getTheme();
 
-  static ThemeData getTheme({Color? primaryColor, Color? secondaryColor}) {
+  static ThemeData getTheme({Color? primaryColor, Color? secondaryColor, Color? backgroundColor}) {
     final baseTheme = ThemeData.light();
     final pColor = primaryColor ?? primary;
     final sColor = secondaryColor ?? secondary;
+    final bg = backgroundColor ?? surface;
 
     // Dynamically compute readable contrast text colors
     final onPrimaryColor = pColor.computeLuminance() > 0.5 ? Color(0xFF2E251B) : Colors.white;
@@ -36,14 +37,14 @@ class AppTheme {
 
     return ThemeData(
       useMaterial3: true,
-      scaffoldBackgroundColor: surface,
+      scaffoldBackgroundColor: bg,
       colorScheme: ColorScheme.light(
         primary: pColor,
         primaryContainer: pColor,
         secondary: sColor,
         secondaryContainer: sColor.withValues(alpha: 0.15),
         onSecondaryContainer: onSecondaryColor,
-        surface: surface,
+        surface: bg,
         onSurface: onSurface,
         onSurfaceVariant: onSurfaceVariant,
         onPrimary: onPrimaryColor,