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)/coach.tsx

@@ -17,7 +17,7 @@ import {
   Text,
   TextInput,
   TouchableOpacity,
-  View,
+  View
 } from 'react-native';
 import Markdown from 'react-native-markdown-display';
 import Animated, { FadeInDown, FadeInUp, Layout } from 'react-native-reanimated';
@@ -32,6 +32,7 @@ import { deleteConversation, getConversationDetail, listConversations, type AiCo
 import { loadAiCoachSessionCache, saveAiCoachSessionCache } from '@/services/aiCoachSession';
 import { api, getAuthToken, postTextStream } from '@/services/api';
 import dayjs from 'dayjs';
+import { LinearGradient } from 'expo-linear-gradient';
 import { ActionSheet } from '../../components/ui/ActionSheet';
 
 type Role = 'user' | 'assistant';
@@ -1121,7 +1122,7 @@ export default function CoachScreen() {
           style={[
             styles.bubble,
             {
-              backgroundColor: isUser ? theme.primary : 'rgba(187,242,70,0.16)',
+              backgroundColor: theme.card, // 16% opacity
               borderTopLeftRadius: isUser ? 16 : 6,
               borderTopRightRadius: isUser ? 6 : 16,
               maxWidth: isUser ? '82%' : '90%',
@@ -1347,7 +1348,7 @@ export default function CoachScreen() {
                         </View>
                       )}
                       {isSelected && isPending && (
-                        <ActivityIndicator size="small" color="#2D5016" />
+                        <ActivityIndicator size="small" color={Colors.light.accentGreenDark} />
                       )}
                       {isSelected && !isPending && (
                         <View style={styles.selectedBadge}>
@@ -1594,7 +1595,13 @@ export default function CoachScreen() {
   }
 
   return (
-    <View style={[styles.screen, { backgroundColor: theme.background }]}>
+    <View style={styles.screen}>
+      <LinearGradient
+        colors={[theme.backgroundGradientStart, theme.backgroundGradientEnd]}
+        style={styles.gradientBackground}
+        start={{ x: 0, y: 0 }}
+        end={{ x: 0, y: 1 }}
+      />
       {/* 顶部标题区域，显示教练名称、新建会话和历史按钮 */}
       <View
         style={[styles.header, { paddingTop: insets.top + 10 }]}
@@ -1608,14 +1615,14 @@ export default function CoachScreen() {
           <TouchableOpacity
             accessibilityRole="button"
             onPress={startNewConversation}
-            style={[styles.headerActionButton, { backgroundColor: 'rgba(187,242,70,0.2)' }]}
+            style={[styles.headerActionButton, { backgroundColor: `${Colors.light.accentGreen}33` }]} // 20% opacity
           >
             <Ionicons name="add-outline" size={18} color={theme.onPrimary} />
           </TouchableOpacity>
           <TouchableOpacity
             accessibilityRole="button"
             onPress={openHistory}
-            style={[styles.headerActionButton, { backgroundColor: 'rgba(187,242,70,0.2)' }]}
+            style={[styles.headerActionButton, { backgroundColor: `${Colors.light.accentGreen}33` }]} // 20% opacity
           >
             <Ionicons name="time-outline" size={18} color={theme.onPrimary} />
           </TouchableOpacity>
@@ -1680,7 +1687,7 @@ export default function CoachScreen() {
           contentContainerStyle={{ paddingHorizontal: 6, gap: 8 }}
         >
           {chips.map((c) => (
-            <TouchableOpacity key={c.key} style={[styles.chip, { borderColor: 'rgba(187,242,70,0.35)', backgroundColor: 'rgba(187,242,70,0.12)' }]} onPress={c.action}>
+            <TouchableOpacity key={c.key} style={[styles.chip, { borderColor: `${Colors.light.accentGreen}59`, backgroundColor: `${Colors.light.accentGreen}1F` }]} onPress={c.action}>
               <Text style={[styles.chipText, { color: '#192126' }]}>{c.label}</Text>
             </TouchableOpacity>
           ))}
@@ -1722,11 +1729,11 @@ export default function CoachScreen() {
           </ScrollView>
         )}
 
-        <View style={[styles.inputRow, { borderColor: 'rgba(187,242,70,0.35)', backgroundColor: 'rgba(187,242,70,0.08)' }]}>
+        <View style={[styles.inputRow, { borderColor: `${Colors.light.accentGreen}59`, backgroundColor: `${Colors.light.accentGreen}14` }]}>
           <TouchableOpacity
             accessibilityRole="button"
             onPress={pickImages}
-            style={[styles.mediaBtn, { backgroundColor: 'rgba(187,242,70,0.16)' }]}
+            style={[styles.mediaBtn, { backgroundColor: `${Colors.light.accentGreen}28` }]}
           >
             <Ionicons name="image-outline" size={18} color={'#192126'} />
           </TouchableOpacity>
@@ -1936,7 +1943,7 @@ const styles = StyleSheet.create({
     borderRadius: 8,
     alignItems: 'center',
     justifyContent: 'center',
-    backgroundColor: 'rgba(187,242,70,0.6)'
+    backgroundColor: `${Colors.light.accentGreen}99` // 60% opacity
   },
   dietOptionsContainer: {
     gap: 8,
@@ -1948,13 +1955,13 @@ const styles = StyleSheet.create({
     borderRadius: 12,
     backgroundColor: 'rgba(255,255,255,0.9)',
     borderWidth: 1,
-    borderColor: 'rgba(187,242,70,0.3)',
+    borderColor: `${Colors.light.accentGreen}4D`, // 30% opacity
   },
   dietOptionIconContainer: {
     width: 40,
     height: 40,
     borderRadius: 20,
-    backgroundColor: 'rgba(187,242,70,0.2)',
+    backgroundColor: `${Colors.light.accentGreen}33`, // 20% opacity
     alignItems: 'center',
     justifyContent: 'center',
     marginRight: 12,
@@ -2003,7 +2010,7 @@ const styles = StyleSheet.create({
     borderRadius: 10,
     alignItems: 'center',
     justifyContent: 'center',
-    backgroundColor: 'rgba(187,242,70,0.6)',
+    backgroundColor: `${Colors.light.accentGreen}99`, // 60% opacity
     alignSelf: 'flex-end',
   },
   // markdown 基础样式承载容器的字体尺寸保持与气泡一致
@@ -2316,17 +2323,17 @@ const styles = StyleSheet.create({
   choiceButton: {
     backgroundColor: 'rgba(255,255,255,0.9)',
     borderWidth: 1,
-    borderColor: 'rgba(187,242,70,0.3)',
+    borderColor: `${Colors.light.accentGreen}4D`, // 30% opacity
     borderRadius: 12,
     padding: 12,
   },
   choiceButtonRecommended: {
-    borderColor: 'rgba(187,242,70,0.6)',
-    backgroundColor: 'rgba(187,242,70,0.1)',
+    borderColor: `${Colors.light.accentGreen}99`, // 60% opacity
+    backgroundColor: `${Colors.light.accentGreen}1A`, // 10% opacity
   },
   choiceButtonSelected: {
-    borderColor: '#2D5016',
-    backgroundColor: 'rgba(187,242,70,0.2)',
+    borderColor: Colors.light.accentGreenDark,
+    backgroundColor: `${Colors.light.accentGreen}33`, // 20% opacity
     borderWidth: 2,
   },
   choiceButtonDisabled: {
@@ -2346,10 +2353,10 @@ const styles = StyleSheet.create({
     flex: 1,
   },
   choiceLabelRecommended: {
-    color: '#2D5016',
+    color: Colors.light.accentGreenDark,
   },
   choiceLabelSelected: {
-    color: '#2D5016',
+    color: Colors.light.accentGreenDark,
     fontWeight: '700',
   },
   choiceLabelDisabled: {
@@ -2361,7 +2368,7 @@ const styles = StyleSheet.create({
     gap: 8,
   },
   recommendedBadge: {
-    backgroundColor: 'rgba(187,242,70,0.8)',
+    backgroundColor: `${Colors.light.accentGreen}CC`, // 80% opacity
     borderRadius: 6,
     paddingHorizontal: 8,
     paddingVertical: 2,
@@ -2369,10 +2376,10 @@ const styles = StyleSheet.create({
   recommendedText: {
     fontSize: 12,
     fontWeight: '700',
-    color: '#2D5016',
+    color: Colors.light.accentGreenDark,
   },
   selectedBadge: {
-    backgroundColor: '#2D5016',
+    backgroundColor: Colors.light.accentGreenDark,
     borderRadius: 6,
     paddingHorizontal: 8,
     paddingVertical: 2,
@@ -2405,6 +2412,13 @@ const styles = StyleSheet.create({
     fontWeight: '600',
     color: '#FF4444',
   },
+  gradientBackground: {
+    position: 'absolute',
+    left: 0,
+    right: 0,
+    top: 0,
+    bottom: 0,
+  },
 });
 
 const markdownStyles = {