feat: 更新 AppNavigator 以自定义导航样式，添加深色主题支持

src/navigation/AppNavigator.tsx

@@ -13,7 +13,17 @@ const Tab = createBottomTabNavigator();
 
 function HomeStackNavigator() {
   return (
-    <HomeStack.Navigator>
+    <HomeStack.Navigator
+      screenOptions={{
+        headerStyle: {
+          backgroundColor: '#1a1a1a',
+        },
+        headerTintColor: '#ffffff',
+        headerTitleStyle: {
+          fontWeight: 'bold',
+        },
+      }}
+    >
       <HomeStack.Screen
         name="TaskList"
         component={TaskListScreen}
@@ -32,6 +42,10 @@ export default function AppNavigator() {
   return (
     <Tab.Navigator
       screenOptions={({ route }) => ({
+        tabBarStyle: {
+          backgroundColor: '#1a1a1a',
+          borderTopColor: '#333',
+        },
         tabBarIcon: ({ color, size }) => {
           let iconName: string;
 
@@ -51,6 +65,7 @@ export default function AppNavigator() {
         },
         tabBarActiveTintColor: '#2196F3',
         tabBarInactiveTintColor: 'gray',
+        headerShown: false,
       })}
     >
       <Tab.Screen