feat(shift): swipeable mini calendar via HorizontalPager

迷你月历接入 HorizontalPager,支持左右滑动翻月:
- 复用主日历 START_PAGE/pageToYearMonth/yearMonthToPage 工具
- viewYear/viewMonth 由 pagerState.currentPage 派生
- 箭头按钮改为 animateScrollToPage
- DatePicker 选月后 animateScrollToPage 跳转
- 网格提取为 MonthGrid 单页组件

core/src/main/kotlin/plus/rua/project/ui/ShiftCalendarGrid.kt

@@ -11,6 +11,8 @@ import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.aspectRatio
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.pager.HorizontalPager
+import androidx.compose.foundation.pager.rememberPagerState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
@@ -28,9 +30,11 @@ import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.material3.rememberDatePickerState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -39,6 +43,7 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
+import kotlinx.coroutines.launch
 import kotlinx.datetime.DatePeriod
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.Month
@@ -75,14 +80,19 @@ fun ShiftCalendarGrid(
     modifier: Modifier = Modifier
 ) {
     val today = remember { Clock.System.todayIn(TimeZone.currentSystemDefault()) }
-    var viewYear by remember { mutableStateOf(today.year) }
-    var viewMonth by remember { mutableStateOf(today.month.number) }
+    val initialYear = remember { today.year }
+    val initialMonth = remember { today.month.number }
     var showMonthPicker by remember { mutableStateOf(false) }
+    val coroutineScope = rememberCoroutineScope()
 
-    // 复用主日历的网格计算(周一为首日,动态行数 4/5/6)
-    val gridInfo = remember(viewYear, viewMonth) { getMonthGridInfo(viewYear, viewMonth) }
-    val firstWeekdayOffset = gridInfo.offset
-    val rows = gridInfo.rows
+    // Pager 居中无限页,与主日历一致;viewYear/viewMonth 由当前页派生
+    val pagerState = rememberPagerState(initialPage = START_PAGE, pageCount = { Int.MAX_VALUE })
+    val viewYear by remember {
+        derivedStateOf { pageToYearMonth(pagerState.currentPage, initialYear, initialMonth).first }
+    }
+    val viewMonth by remember {
+        derivedStateOf { pageToYearMonth(pagerState.currentPage, initialYear, initialMonth).second }
+    }
 
     Card(
         modifier = modifier.fillMaxWidth(),
@@ -97,7 +107,7 @@ fun ShiftCalendarGrid(
                 verticalAlignment = Alignment.CenterVertically
             ) {
                 IconButton(onClick = {
-                    if (viewMonth == 1) { viewMonth = 12; viewYear -= 1 } else viewMonth -= 1
+                    coroutineScope.launch { pagerState.animateScrollToPage(pagerState.currentPage - 1) }
                 }) {
                     Icon(Icons.Filled.ChevronLeft, contentDescription = "上个月")
                 }
@@ -108,7 +118,7 @@ fun ShiftCalendarGrid(
                     modifier = Modifier.clickable { showMonthPicker = true }
                 )
                 IconButton(onClick = {
-                    if (viewMonth == 12) { viewMonth = 1; viewYear += 1 } else viewMonth += 1
+                    coroutineScope.launch { pagerState.animateScrollToPage(pagerState.currentPage + 1) }
                 }) {
                     Icon(Icons.Filled.ChevronRight, contentDescription = "下个月")
                 }
@@ -127,25 +137,20 @@ fun ShiftCalendarGrid(
                 }
             }
 
-            (0 until rows).forEach { row ->
-                Row(Modifier.fillMaxWidth()) {
-                    (0 until 7).forEach { col ->
-                        val cellIndex = row * 7 + col
-                        val dayNum = cellIndex - firstWeekdayOffset + 1
-                        if (dayNum in 1..gridInfo.daysInMonth) {
-                            val date = LocalDate(viewYear, Month(viewMonth), dayNum)
-                            ShiftDayCell(
-                                date = date,
+            // 滑动翻页区域:每页一个月的网格
+            HorizontalPager(
+                state = pagerState,
+                beyondViewportPageCount = 0,
+                modifier = Modifier.fillMaxWidth()
+            ) { page ->
+                val (year, month) = pageToYearMonth(page, initialYear, initialMonth)
+                MonthGrid(
+                    year = year,
+                    month = month,
                     pattern = pattern,
-                                onClick = { onPatternChange(toggleOverride(pattern, date)) },
-                                onLongClick = { onPatternChange(toggleFlipAndRephase(pattern, date)) },
-                                modifier = Modifier.weight(1f)
+                    onPatternChange = onPatternChange,
+                    modifier = Modifier.fillMaxWidth()
                 )
-                        } else {
-                            Box(Modifier.weight(1f).aspectRatio(1f))
-                        }
-                    }
-                }
             }
         }
     }
@@ -161,8 +166,10 @@ fun ShiftCalendarGrid(
                 TextButton(onClick = {
                     datePickerState.selectedDateMillis?.let { millis ->
                         val picked = millis.toLocalDate()
-                        viewYear = picked.year
-                        viewMonth = picked.month.number
+                        val targetPage = yearMonthToPage(
+                            picked.year, picked.month.number, initialYear, initialMonth
+                        )
+                        coroutineScope.launch { pagerState.animateScrollToPage(targetPage) }
                     }
                     showMonthPicker = false
                 }) { Text("确定") }
@@ -176,6 +183,48 @@ fun ShiftCalendarGrid(
     }
 }
 
+/**
+ * 迷你月历的单页网格。复用主日历 [getMonthGridInfo] 计算行数与偏移。
+ *
+ * @param year 年
+ * @param month 月(1-12)
+ * @param pattern 当前轮班配置(只读)
+ * @param onPatternChange 修改后的新 pattern 回调
+ * @param modifier 外部布局修饰符
+ */
+@Composable
+private fun MonthGrid(
+    year: Int,
+    month: Int,
+    pattern: ShiftPattern,
+    onPatternChange: (ShiftPattern) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    val gridInfo = remember(year, month) { getMonthGridInfo(year, month) }
+    Column(modifier) {
+        (0 until gridInfo.rows).forEach { row ->
+            Row(Modifier.fillMaxWidth()) {
+                (0 until 7).forEach { col ->
+                    val cellIndex = row * 7 + col
+                    val dayNum = cellIndex - gridInfo.offset + 1
+                    if (dayNum in 1..gridInfo.daysInMonth) {
+                        val date = LocalDate(year, Month(month), dayNum)
+                        ShiftDayCell(
+                            date = date,
+                            pattern = pattern,
+                            onClick = { onPatternChange(toggleOverride(pattern, date)) },
+                            onLongClick = { onPatternChange(toggleFlipAndRephase(pattern, date)) },
+                            modifier = Modifier.weight(1f)
+                        )
+                    } else {
+                        Box(Modifier.weight(1f).aspectRatio(1f))
+                    }
+                }
+            }
+        }
+    }
+}
+
 /**
  * 翻转某天的班/休(单日 override)。翻转后若与基础周期值一致,则移除 override。
  *