feat: 新增目标管理功能及相关组件

- 创建目标管理演示页面，展示高保真的目标管理界面
- 实现待办事项卡片的横向滑动展示，支持时间筛选功能
- 新增时间轴组件，展示选中日期的具体任务
- 更新底部导航，添加目标管理和演示页面的路由
- 优化个人页面菜单项，提供目标管理的快速访问
- 编写目标管理功能实现文档，详细描述功能和组件架构

app/(tabs)/_layout.tsx

@@ -21,6 +21,7 @@ export default function TabLayout() {
         const routeName = route.name;
         const isSelected = (routeName === 'explore' && pathname === ROUTES.TAB_EXPLORE) ||
           (routeName === 'coach' && pathname === ROUTES.TAB_COACH) ||
+          (routeName === 'goals' && pathname === ROUTES.TAB_GOALS) ||
           (routeName === 'statistics' && pathname === ROUTES.TAB_STATISTICS) ||
           pathname.includes(routeName);
 
@@ -44,6 +45,8 @@ export default function TabLayout() {
                   return { icon: 'magnifyingglass.circle.fill', title: '发现' } as const;
                 case 'coach':
                   return { icon: 'person.3.fill', title: 'Seal' } as const;
+                case 'goals':
+                  return { icon: 'flag.fill', title: '目标' } as const;
                 case 'statistics':
                   return { icon: 'chart.pie.fill', title: '统计' } as const;
                 case 'personal':
@@ -185,6 +188,7 @@ export default function TabLayout() {
           },
         }}
       />
+
       <Tabs.Screen
         name="statistics"
         options={{
@@ -213,7 +217,34 @@ export default function TabLayout() {
           },
         }}
       />
-
+      <Tabs.Screen
+        name="goals"
+        options={{
+          title: '目标',
+          tabBarIcon: ({ color }) => {
+            const isGoalsSelected = pathname === '/goals';
+            return (
+              <View style={{ flexDirection: 'row', alignItems: 'center' }}>
+                <IconSymbol size={22} name="flag.fill" color={color} />
+                {isGoalsSelected && (
+                  <Text
+                    numberOfLines={1}
+                    style={{
+                      color: color,
+                      fontSize: 12,
+                      fontWeight: '600',
+                      marginLeft: 6,
+                      textAlign: 'center',
+                      flexShrink: 0,
+                    }}>
+                    目标
+                  </Text>
+                )}
+              </View>
+            );
+          },
+        }}
+      />
       <Tabs.Screen
         name="personal"
         options={{