feat: implement splash and onboarding flows, update app assets, and add project design documentation

apps/rider/lib/core/design/theme.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import '../build_config.dart';
 import 'tripz_colors.dart';
 import 'typography.dart';
 
@@ -6,7 +7,7 @@ import 'typography.dart';
 /// docs/26 §2, §4
 ThemeData buildTheme({required Brightness brightness, required Locale locale}) {
   final bool isDark = brightness == Brightness.dark;
-  final seed = const Color(0xFF0E7C66); // أخضر تركوازي — بذرة المستأجر
+  final seed = Color(BuildConfig.primaryColorValue); // أخضر تركوازي — بذرة المستأجر
 
   final colorScheme = ColorScheme.fromSeed(
     seedColor: seed,