feat(ui): 统一应用主题色为天空蓝并优化渐变背景

将应用主色调从 '#BBF246' 更改为 '#87CEEB'（天空蓝），并更新所有相关组件和页面中的颜色引用。同时为多个页面添加统一的渐变背景，提升视觉效果和用户体验。新增压力分析模态框组件，并优化压力计组件的交互与显示逻辑。更新应用图标和启动图资源。

app/(tabs)/statistics.tsx

@@ -3,6 +3,7 @@ import { BMICard } from '@/components/BMICard';
 import { CircularRing } from '@/components/CircularRing';
 import { NutritionRadarCard } from '@/components/NutritionRadarCard';
 import { ProgressBar } from '@/components/ProgressBar';
+import { StressAnalysisModal } from '@/components/StressAnalysisModal';
 import { StressMeter } from '@/components/StressMeter';
 import { WeightHistoryCard } from '@/components/WeightHistoryCard';
 import { Colors } from '@/constants/Colors';
@@ -17,6 +18,7 @@ import { Ionicons } from '@expo/vector-icons';
 import { useBottomTabBarHeight } from '@react-navigation/bottom-tabs';
 import { useFocusEffect } from '@react-navigation/native';
 import dayjs from 'dayjs';
+import { LinearGradient } from 'expo-linear-gradient';
 import React, { useEffect, useMemo, useRef, useState } from 'react';
 import {
   SafeAreaView,
@@ -85,6 +87,9 @@ export default function ExploreScreen() {
   const [nutritionSummary, setNutritionSummary] = useState<NutritionSummary | null>(null);
   const [isNutritionLoading, setIsNutritionLoading] = useState(false);
 
+  // 压力分析浮窗状态
+  const [showStressModal, setShowStressModal] = useState(false);
+
   // 记录最近一次请求的“日期键”，避免旧请求覆盖新结果
   const latestRequestKeyRef = useRef<string | null>(null);
 
@@ -110,7 +115,7 @@ export default function ExploreScreen() {
       } else {
         derivedDate = days[selectedIndex]?.date?.toDate() ?? new Date();
       }
-      
+
       const requestKey = getDateKey(derivedDate);
       latestRequestKeyRef.current = requestKey;
 
@@ -204,10 +209,28 @@ export default function ExploreScreen() {
     }
   };
 
+  // 处理压力卡片点击
+  const handleStressCardPress = () => {
+    setShowStressModal(true);
+  };
+
+  // 关闭压力分析浮窗
+  const handleCloseStressModal = () => {
+    setShowStressModal(false);
+  };
+
+  // 使用统一的渐变背景色
+  const backgroundGradientColors = [colorTokens.backgroundGradientStart, colorTokens.backgroundGradientEnd] as const;
 
   return (
-    <View style={[styles.container, { backgroundColor: theme === 'light' ? colorTokens.pageBackgroundEmphasis : colorTokens.background }]}>
-      <SafeAreaView style={[styles.safeArea, { backgroundColor: theme === 'light' ? colorTokens.pageBackgroundEmphasis : colorTokens.background }]}>
+    <View style={styles.container}>
+      <LinearGradient
+        colors={backgroundGradientColors}
+        style={styles.gradientBackground}
+        start={{ x: 0, y: 0 }}
+        end={{ x: 0, y: 1 }}
+      />
+      <SafeAreaView style={styles.safeArea}>
         <ScrollView
           style={styles.scrollView}
           contentContainerStyle={{ paddingBottom: bottomPadding }}
@@ -253,12 +276,13 @@ export default function ExploreScreen() {
           <View style={styles.masonryContainer}>
             {/* 左列 */}
             <View style={styles.masonryColumn}>
-              <StressMeter 
-                value={hrvValue} 
+              <StressMeter
+                value={hrvValue}
                 updateTime={hrvUpdateTime}
                 style={styles.masonryCard}
+                onPress={handleStressCardPress}
               />
-              
+
               <View style={[styles.masonryCard, styles.caloriesCard]}>
                 <Text style={styles.cardTitleSecondary}>消耗卡路里</Text>
                 {activeCalories != null ? (
@@ -306,20 +330,20 @@ export default function ExploreScreen() {
                 weight={userProfile?.weight ? parseFloat(userProfile.weight) : undefined}
                 height={userProfile?.height ? parseFloat(userProfile.height) : undefined}
                 style={styles.masonryCardNoBg}
-                compact={true}
+              // compact={true}
               />
 
               <View style={[styles.masonryCard, styles.trainingCard]}>
                 <Text style={styles.cardTitleSecondary}>训练时间</Text>
                 <View style={styles.trainingContent}>
-                                      <CircularRing
-                      size={120}
-                      strokeWidth={12}
-                      trackColor="#E2D9FD"
-                      progressColor="#8B74F3"
-                      progress={trainingProgress}
-                      resetToken={animToken}
-                    />
+                  <CircularRing
+                    size={120}
+                    strokeWidth={12}
+                    trackColor="#E2D9FD"
+                    progressColor="#8B74F3"
+                    progress={trainingProgress}
+                    resetToken={animToken}
+                  />
                 </View>
               </View>
 
@@ -347,16 +371,32 @@ export default function ExploreScreen() {
 
         </ScrollView>
       </SafeAreaView>
+
+      {/* 压力分析浮窗 */}
+      <StressAnalysisModal
+        visible={showStressModal}
+        onClose={handleCloseStressModal}
+        hrvValue={hrvValue}
+        updateTime={hrvUpdateTime}
+      />
     </View>
   );
 }
 
 const primary = Colors.light.primary;
+const lightColors = Colors.light;
+const darkColors = Colors.dark;
 
 const styles = StyleSheet.create({
   container: {
     flex: 1,
-    backgroundColor: '#F6F7F8',
+  },
+  gradientBackground: {
+    position: 'absolute',
+    left: 0,
+    right: 0,
+    top: 0,
+    bottom: 0,
   },
   safeArea: {
     flex: 1,
@@ -388,10 +428,10 @@ const styles = StyleSheet.create({
     justifyContent: 'center',
   },
   dayPillNormal: {
-    backgroundColor: '#C8F852',
+    backgroundColor: lightColors.datePickerNormal,
   },
   dayPillSelected: {
-    backgroundColor: '#192126',
+    backgroundColor: lightColors.datePickerSelected,
   },
   dayLabel: {
     fontSize: 16,
@@ -414,7 +454,7 @@ const styles = StyleSheet.create({
     width: 8,
     height: 8,
     borderRadius: 4,
-    backgroundColor: '#192126',
+    backgroundColor: lightColors.datePickerSelected,
     marginTop: 10,
     marginBottom: 4,
     alignSelf: 'center',