Implement multi-screen app UI flow and navigation

lib/core/config/app_config.dart

@@ -20,7 +20,7 @@ class AppConfig {
 
   /// Enables fake backend implementation for local/offline development.
   static bool get useFakeBackend =>
-      const bool.fromEnvironment('USE_FAKE_BACKEND', defaultValue: false);
+      const bool.fromEnvironment('USE_FAKE_BACKEND', defaultValue: true);
 
   /// Runtime override for backend URL (e.g. local settings screen).
   static void overrideBackendBaseUrl(String? baseUrl) {

lib/core/config/app_theme.dart

@@ -4,31 +4,55 @@ import 'package:flutter/material.dart';
 class AppTheme {
   AppTheme._();
 
-  static const Color background = Color(0xFFEDF0F2);
+  static const Color background = Color(0xFFF3F6F8);
   static const Color surface = Color(0xFFFFFFFF);
-  static const Color primary = Color(0xFF253840);
-  static const Color accent = Color(0xFF00B6F0);
+  static const Color primary = Color(0xFF1E3541);
+  static const Color accent = Color(0xFF1AB6C8);
+  static const Color textPrimary = Color(0xFF18303A);
+  static const Color textSecondary = Color(0xFF58707A);
 
   /// Builds the Material [ThemeData].
   static ThemeData light() {
-    final ColorScheme colorScheme = ColorScheme.fromSeed(
-      seedColor: primary,
-      primary: primary,
-      secondary: accent,
-      surface: surface,
-      brightness: Brightness.light,
+    final ColorScheme colorScheme = ColorScheme.fromSeed(seedColor: primary);
+    final TextTheme textTheme = ThemeData.light().textTheme.apply(
+      fontFamily: 'WorkSans',
+      bodyColor: textPrimary,
+      displayColor: textPrimary,
     );
 
     return ThemeData(
       useMaterial3: true,
-      colorScheme: colorScheme,
+      colorScheme: colorScheme.copyWith(
+        primary: primary,
+        secondary: accent,
+        surface: surface,
+      ),
       scaffoldBackgroundColor: background,
+      textTheme: textTheme.copyWith(
+        headlineMedium: textTheme.headlineMedium?.copyWith(
+          fontWeight: FontWeight.w700,
+          letterSpacing: 0.1,
+        ),
+        titleLarge: textTheme.titleLarge?.copyWith(
+          fontWeight: FontWeight.w700,
+          letterSpacing: 0.1,
+        ),
+        titleMedium: textTheme.titleMedium?.copyWith(
+          fontWeight: FontWeight.w600,
+        ),
+      ),
       appBarTheme: const AppBarTheme(
         centerTitle: false,
-        backgroundColor: surface,
-        foregroundColor: primary,
+        backgroundColor: Colors.transparent,
+        foregroundColor: textPrimary,
         elevation: 0,
       ),
+      cardTheme: CardThemeData(
+        color: surface,
+        elevation: 0,
+        margin: EdgeInsets.zero,
+        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(24)),
+      ),
     );
   }
 }