feat: 引入路由常量并更新相关页面导航

- 新增 ROUTES 常量文件，集中管理应用路由
- 更新多个页面的导航逻辑，使用 ROUTES 常量替代硬编码路径
- 修改教练页面和今日训练页面的路由，提升代码可维护性
- 优化标签页和登录页面的导航，确保一致性和易用性

app/(tabs)/index.tsx

@@ -16,6 +16,7 @@ import { useRouter } from 'expo-router';
 import React from 'react';
 import { Animated, Image, PanResponder, Pressable, SafeAreaView, ScrollView, StyleSheet, useWindowDimensions, View } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import { ROUTES, QUERY_PARAMS, ROUTE_PARAMS } from '@/constants/Routes';
 
 // 移除旧的“热门活动”滑动数据，改为固定的“热点功能”卡片
 
@@ -76,7 +77,7 @@ export default function HomeScreen() {
       Animated.spring(pan, { toValue: { x: snapX, y: clampedY }, useNativeDriver: false, bounciness: 6 }).start(() => {
         if (!dragState.current.moved) {
           // 切换到教练 tab，并传递name参数
-          router.push('/coach?name=Iris' as any);
+          router.push(`${ROUTES.TAB_COACH}?${QUERY_PARAMS.COACH_NAME}=Iris` as any);
         }
       });
     },
@@ -113,7 +114,7 @@ export default function HomeScreen() {
         title: '今日训练',
         subtitle: '完成一次普拉提训练，记录你的坚持',
         level: '初学者',
-        onPress: () => pushIfAuthedElseLogin('/workout/today'),
+        onPress: () => pushIfAuthedElseLogin(ROUTES.WORKOUT_TODAY),
       },
       {
         type: 'plan',
@@ -123,7 +124,7 @@ export default function HomeScreen() {
         title: '体态评估',
         subtitle: '评估你的体态，制定训练计划',
         level: '初学者',
-        onPress: () => router.push('/ai-posture-assessment'),
+        onPress: () => router.push(ROUTES.AI_POSTURE_ASSESSMENT),
       },
       ...listRecommendedArticles().map((a) => ({
         type: 'article' as const,
@@ -185,7 +186,7 @@ export default function HomeScreen() {
               image: 'https://plates-1251306435.cos.ap-guangzhou.myqcloud.com/images/imagedemo.jpeg',
               title: c.title || '今日训练',
               subtitle: c.subtitle || '完成一次普拉提训练，记录你的坚持',
-              onPress: () => pushIfAuthedElseLogin('/workout/today'),
+              onPress: () => pushIfAuthedElseLogin(ROUTES.WORKOUT_TODAY),
             });
           }
         }
@@ -204,7 +205,7 @@ export default function HomeScreen() {
   const handlePlanCardPress = () => {
     if (activePlan) {
       // 跳转到训练计划页面的锻炼tab，并传递planId参数
-      router.push(`/training-plan?planId=${activePlan.id}&tab=schedule` as any);
+      router.push(`${ROUTES.TRAINING_PLAN}?${ROUTE_PARAMS.TRAINING_PLAN_ID}=${activePlan.id}&${ROUTE_PARAMS.TRAINING_PLAN_TAB}=${QUERY_PARAMS.TRAINING_PLAN_TAB_SCHEDULE}` as any);
     }
   };
 
@@ -275,7 +276,7 @@ export default function HomeScreen() {
 
               <Pressable
                 style={[styles.featureCard, styles.featureCardQuinary]}
-                onPress={() => pushIfAuthedElseLogin('/workout/today')}
+                onPress={() => pushIfAuthedElseLogin(ROUTES.WORKOUT_TODAY)}
               >
                 <View style={styles.featureIconWrapper}>
                   <View style={styles.featureIconPlaceholder}>
@@ -290,7 +291,7 @@ export default function HomeScreen() {
 
               <Pressable
                 style={[styles.featureCard, styles.featureCardPrimary]}
-                onPress={() => pushIfAuthedElseLogin('/ai-posture-assessment')}
+                onPress={() => pushIfAuthedElseLogin(ROUTES.AI_POSTURE_ASSESSMENT)}
               >
                 <View style={styles.featureIconWrapper}>
                   <Image
@@ -303,7 +304,7 @@ export default function HomeScreen() {
 
               <Pressable
                 style={[styles.featureCard, styles.featureCardQuaternary]}
-                onPress={() => pushIfAuthedElseLogin('/training-plan')}
+                onPress={() => pushIfAuthedElseLogin(ROUTES.TRAINING_PLAN)}
               >
                 <View style={styles.featureIconWrapper}>
                   <View style={styles.featureIconPlaceholder}>