feat: 添加教练功能和更新用户界面

- 新增教练页面，用户可以与教练进行互动和咨询
- 更新首页，切换到教练 tab 并传递名称参数
- 优化个人信息页面，添加注销帐号和退出登录功能
- 更新隐私政策和用户协议的链接，确保用户在使用前同意相关条款
- 修改今日训练页面标题为“开始训练”，提升用户体验
- 删除不再使用的进度条组件，简化代码结构

app/(tabs)/_layout.tsx

@@ -18,6 +18,7 @@ export default function TabLayout() {
       screenOptions={({ route }) => {
         const routeName = route.name;
         const isSelected = (routeName === 'index' && pathname === '/') ||
+          (routeName === 'coach' && pathname === '/coach') ||
           (routeName === 'explore' && pathname === '/explore') ||
           pathname.includes(routeName);
 
@@ -39,6 +40,8 @@ export default function TabLayout() {
               switch (routeName) {
                 case 'index':
                   return { icon: 'house.fill', title: '首页' } as const;
+                case 'coach':
+                  return { icon: 'person.3.fill', title: '教练' } as const;
                 case 'explore':
                   return { icon: 'paperplane.fill', title: '探索' } as const;
                 case 'personal':
@@ -150,6 +153,34 @@ export default function TabLayout() {
           },
         }}
       />
+      <Tabs.Screen
+        name="coach"
+        options={{
+          title: '教练',
+          tabBarIcon: ({ color }) => {
+            const isCoachSelected = pathname === '/coach';
+            return (
+              <View style={{ flexDirection: 'row', alignItems: 'center' }}>
+                <IconSymbol size={22} name="person.3.fill" color={color} />
+                {isCoachSelected && (
+                  <Text
+                    numberOfLines={1}
+                    style={{
+                      color: color,
+                      fontSize: 12,
+                      fontWeight: '600',
+                      marginLeft: 6,
+                      textAlign: 'center',
+                      flexShrink: 0,
+                    }}>
+                    教练
+                  </Text>
+                )}
+              </View>
+            );
+          },
+        }}
+      />
       <Tabs.Screen
         name="explore"
         options={{