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/challenge/day.tsx

@@ -1,4 +1,5 @@
 import { HeaderBar } from '@/components/ui/HeaderBar';
+import { Colors } from '@/constants/Colors';
 import { useAppDispatch, useAppSelector } from '@/hooks/redux';
 import { completeDay, setCustom } from '@/store/challengeSlice';
 import type { Exercise, ExerciseCustomConfig } from '@/utils/pilatesPlan';
@@ -158,7 +159,7 @@ const styles = StyleSheet.create({
   counterValue: { minWidth: 40, textAlign: 'center', fontWeight: '700', color: '#111827' },
   setPill: { paddingHorizontal: 10, paddingVertical: 6, borderRadius: 999 },
   setPillTodo: { backgroundColor: '#F3F4F6' },
-  setPillDone: { backgroundColor: '#BBF246' },
+  setPillDone: { backgroundColor: Colors.light.accentGreen },
   setPillText: { fontSize: 12, fontWeight: '700' },
   setPillTextTodo: { color: '#6B7280' },
   setPillTextDone: { color: '#192126' },
@@ -167,7 +168,7 @@ const styles = StyleSheet.create({
   tipsBox: { marginTop: 10, backgroundColor: '#F9FAFB', borderRadius: 8, padding: 10 },
   tipText: { fontSize: 12, color: '#6B7280', lineHeight: 18 },
   bottomBar: { position: 'absolute', left: 0, right: 0, bottom: 0, padding: 20, backgroundColor: 'transparent' },
-  finishBtn: { backgroundColor: '#BBF246', paddingVertical: 14, borderRadius: 999, alignItems: 'center' },
+  finishBtn: { backgroundColor: Colors.light.accentGreen, paddingVertical: 14, borderRadius: 999, alignItems: 'center' },
   finishBtnText: { color: '#192126', fontWeight: '800', fontSize: 16 },
 });