feat: 优化 AI 教练聊天和打卡功能

- 在 AI 教练聊天界面中添加会话缓存功能，支持冷启动时恢复聊天记录
- 实现轻量防抖机制，确保会话变动时及时保存缓存
- 在打卡功能中集成按月加载打卡记录，提升用户体验
- 更新 Redux 状态管理，支持打卡记录的按月加载和缓存
- 新增打卡日历页面，允许用户查看每日打卡记录
- 优化样式以适应新功能的展示和交互

app/checkin/calendar.tsx

@@ -0,0 +1,122 @@
+import { HeaderBar } from '@/components/ui/HeaderBar';
+import { Colors } from '@/constants/Colors';
+import { useAppDispatch, useAppSelector } from '@/hooks/redux';
+import { useColorScheme } from '@/hooks/useColorScheme';
+import { DailyStatusItem, fetchDailyStatusRange } from '@/services/checkins';
+import { getDailyCheckins, loadMonthCheckins, setCurrentDate } from '@/store/checkinSlice';
+import { getMonthDaysZh } from '@/utils/date';
+import dayjs from 'dayjs';
+import { useRouter } from 'expo-router';
+import React, { useEffect, useMemo, useState } from 'react';
+import { Dimensions, FlatList, SafeAreaView, StyleSheet, Text, TouchableOpacity, View } from 'react-native';
+import { useSafeAreaInsets } from 'react-native-safe-area-context';
+
+function formatDate(d: Date) {
+  const y = d.getFullYear();
+  const m = `${d.getMonth() + 1}`.padStart(2, '0');
+  const day = `${d.getDate()}`.padStart(2, '0');
+  return `${y}-${m}-${day}`;
+}
+
+export default function CheckinCalendarScreen() {
+  const router = useRouter();
+  const theme = (useColorScheme() ?? 'light') as 'light' | 'dark';
+  const colorTokens = Colors[theme];
+  const dispatch = useAppDispatch();
+  const checkin = useAppSelector((s) => (s as any).checkin);
+  const insets = useSafeAreaInsets();
+
+  const [cursor, setCursor] = useState(dayjs());
+  const days = useMemo(() => getMonthDaysZh(cursor), [cursor]);
+  const monthTitle = useMemo(() => `${cursor.format('YYYY年M月')} 打卡`, [cursor]);
+  const [statusMap, setStatusMap] = useState<Record<string, boolean>>({});
+
+  useEffect(() => {
+    dispatch(loadMonthCheckins({ year: cursor.year(), month1Based: cursor.month() + 1 }));
+    const y = cursor.year();
+    const m = cursor.month() + 1;
+    const pad = (n: number) => `${n}`.padStart(2, '0');
+    const startDate = `${y}-${pad(m)}-01`;
+    const endDate = `${y}-${pad(m)}-${pad(new Date(y, m, 0).getDate())}`;
+    fetchDailyStatusRange(startDate, endDate)
+      .then((list: DailyStatusItem[]) => {
+        const next: Record<string, boolean> = {};
+        for (const it of list) {
+          if (typeof it?.date === 'string') next[it.date] = !!it?.checkedIn;
+        }
+        setStatusMap(next);
+      })
+      .catch(() => setStatusMap({}));
+  }, [cursor, dispatch]);
+
+  const goPrevMonth = () => setCursor((c) => c.subtract(1, 'month'));
+  const goNextMonth = () => setCursor((c) => c.add(1, 'month'));
+
+  return (
+    <SafeAreaView style={[styles.safeArea, { backgroundColor: theme === 'light' ? colorTokens.pageBackgroundEmphasis : colorTokens.background }]}>
+      <View style={[styles.container, { backgroundColor: theme === 'light' ? colorTokens.pageBackgroundEmphasis : colorTokens.background }]}>
+        <HeaderBar title="打卡日历" onBack={() => router.back()} withSafeTop={false} transparent />
+        <View style={styles.headerRow}>
+          <TouchableOpacity style={[styles.monthBtn, { backgroundColor: colorTokens.card }]} onPress={goPrevMonth}><Text style={[styles.monthBtnText, { color: colorTokens.text }]}>上一月</Text></TouchableOpacity>
+          <Text style={[styles.monthTitle, { color: colorTokens.text }]}>{monthTitle}</Text>
+          <TouchableOpacity style={[styles.monthBtn, { backgroundColor: colorTokens.card }]} onPress={goNextMonth}><Text style={[styles.monthBtnText, { color: colorTokens.text }]}>下一月</Text></TouchableOpacity>
+        </View>
+
+        <FlatList
+          data={days}
+          keyExtractor={(item) => item.date.format('YYYY-MM-DD')}
+          numColumns={5}
+          columnWrapperStyle={{ justifyContent: 'space-between', marginBottom: 12 }}
+          contentContainerStyle={{ paddingHorizontal: 20, paddingTop: 10, paddingBottom: insets.bottom + 20 }}
+          renderItem={({ item }) => {
+            const d = item.date.toDate();
+            const dateStr = formatDate(d);
+            const hasAny = statusMap[dateStr] ?? !!(checkin?.byDate?.[dateStr]?.items?.length);
+            const isToday = formatDate(new Date()) === dateStr;
+            return (
+              <TouchableOpacity
+                onPress={async () => {
+                  dispatch(setCurrentDate(dateStr));
+                  await dispatch(getDailyCheckins(dateStr));
+                  router.push('/checkin');
+                }}
+                activeOpacity={0.8}
+                style={[styles.dayCell, { backgroundColor: colorTokens.card }, hasAny && styles.dayCellCompleted, isToday && styles.dayCellToday]}
+              >
+                <Text style={[styles.dayNumber, { color: colorTokens.text }]}>{item.dayOfMonth}</Text>
+                {hasAny && <View style={styles.dot} />}
+              </TouchableOpacity>
+            );
+          }}
+        />
+      </View>
+    </SafeAreaView>
+  );
+}
+
+const { width } = Dimensions.get('window');
+const cellSize = (width - 40 - 4 * 12) / 5; // 20 padding *2, 12 spacing *4
+
+const styles = StyleSheet.create({
+  safeArea: { flex: 1, backgroundColor: '#F7F8FA' },
+  container: { flex: 1, backgroundColor: '#F7F8FA' },
+  headerRow: { flexDirection: 'row', alignItems: 'center', justifyContent: 'space-between', paddingHorizontal: 20, paddingTop: 6 },
+  monthTitle: { fontSize: 18, fontWeight: '800' },
+  monthBtn: { paddingHorizontal: 12, paddingVertical: 8, borderRadius: 999 },
+  monthBtnText: { fontWeight: '700' },
+  dayCell: {
+    width: cellSize,
+    height: cellSize,
+    borderRadius: 16,
+    alignItems: 'center',
+    justifyContent: 'center',
+    shadowColor: '#000', shadowOpacity: 0.06, shadowRadius: 12, shadowOffset: { width: 0, height: 6 }, elevation: 3,
+    position: 'relative',
+  },
+  dayCellCompleted: { backgroundColor: '#ECFDF5', borderWidth: 1, borderColor: '#A7F3D0' },
+  dayCellToday: { borderWidth: 1, borderColor: '#BBF246' },
+  dayNumber: { fontWeight: '800', fontSize: 16 },
+  dot: { position: 'absolute', top: 6, right: 6, width: 8, height: 8, borderRadius: 4, backgroundColor: '#10B981' },
+});
+
+