feat(TabsLayout): add schedule tab with calendar icon

- Introduced a new "schedule" tab in the TabsLayout component, enhancing navigation options for users.
- Configured the tab with a title and a calendar icon for improved visual representation.
- Removed the previous implementation of the schedule tab to streamline the codebase.

app/(app)/(tabs)/_layout.tsx

@@ -61,6 +61,15 @@ export default function TabsLayout() {
           ),
         }}
       />
+      <Tabs.Screen
+        name="schedule"
+        options={{
+          title: '课表',
+          tabBarIcon: ({ color, focused }) => (
+            <MaterialCommunityIcons name="calendar-today" size={focused ? 24 : 22} color={color} />
+          ),
+        }}
+      />
       <Tabs.Screen
         name="messages"
         options={{
@@ -75,15 +84,6 @@ export default function TabsLayout() {
           ),
         }}
       />
-      <Tabs.Screen
-        name="schedule"
-        options={{
-          title: '课表',
-          tabBarIcon: ({ color, focused }) => (
-            <MaterialCommunityIcons name="calendar-today" size={focused ? 24 : 22} color={color} />
-          ),
-        }}
-      />
       <Tabs.Screen
         name="profile"
         options={{