feat: 添加心情记录功能

在统计页面新增心情卡片和弹窗组件，支持用户记录和查看每日心情状态。

components/MoodCard.tsx

@@ -0,0 +1,76 @@
+import React from 'react';
+import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
+import { ThemedText } from './ThemedText';
+import { ThemedView } from './ThemedView';
+
+interface MoodCardProps {
+  onPress: () => void;
+}
+
+export function MoodCard({ onPress }: MoodCardProps) {
+  return (
+    <ThemedView style={styles.container}>
+      <View style={styles.header}>
+        <ThemedText style={styles.title}>心情</ThemedText>
+        <ThemedText style={styles.subtitle}>记录你的每日心情</ThemedText>
+      </View>
+
+      <TouchableOpacity style={styles.content} onPress={onPress}>
+        <View style={styles.moodIcon}>
+          <Text style={styles.emoji}>😊</Text>
+        </View>
+        <ThemedText style={styles.moodText}>点击记录今日心情</ThemedText>
+      </TouchableOpacity>
+    </ThemedView>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    backgroundColor: '#fff',
+    borderRadius: 16,
+    padding: 16,
+    marginBottom: 16,
+    shadowColor: '#000',
+    shadowOffset: {
+      width: 0,
+      height: 2,
+    },
+    shadowOpacity: 0.1,
+    shadowRadius: 3.84,
+    elevation: 5,
+  },
+  header: {
+    marginBottom: 12,
+  },
+  title: {
+    fontSize: 18,
+    fontWeight: '600',
+    marginBottom: 4,
+  },
+  subtitle: {
+    fontSize: 14,
+    opacity: 0.6,
+  },
+  content: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    paddingVertical: 8,
+  },
+  moodIcon: {
+    width: 40,
+    height: 40,
+    borderRadius: 20,
+    backgroundColor: '#f0f0f0',
+    justifyContent: 'center',
+    alignItems: 'center',
+    marginRight: 12,
+  },
+  emoji: {
+    fontSize: 20,
+  },
+  moodText: {
+    fontSize: 16,
+    flex: 1,
+  },
+});