feat: 底部卡片显示班次状态提示

根据选中日期的班次类型（WORK/OFF）在底部卡片展示对应提示语。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

shared/src/commonMain/kotlin/plus/rua/project/ui/BottomCard.kt

@@ -26,6 +26,7 @@ import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import kotlinx.datetime.LocalDate
 import plus.rua.project.CalendarViewModel
+import plus.rua.project.ShiftKind
 
 /**
  * 底部卡片，折叠状态下支持垂直拖拽触发折叠动画。
@@ -55,6 +56,11 @@ fun BottomCard(
     @Suppress("DEPRECATION") // monthNumber 无替代 API，kotlinx-datetime 尚未提供新接口
     val solarDesc = "${selectedDate.monthNumber}月${selectedDate.day}日"
     val lunarDesc = formatLunarDate(selectedDate)
+    val shiftMessage = when (viewModel.shiftKindAt(selectedDate)) {
+        ShiftKind.WORK -> "小小上班，轻松拿下！"
+        ShiftKind.OFF -> "耶耶耶，美美休息！"
+        null -> null
+    }
 
     Surface(
         modifier = modifier
@@ -147,6 +153,17 @@ fun BottomCard(
                     fontSize = 14.sp
                 )
             }
+            if (shiftMessage != null) {
+                Text(
+                    text = shiftMessage,
+                    modifier = Modifier
+                        .align(Alignment.CenterHorizontally)
+                        .padding(top = 12.dp, bottom = 6.dp),
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    fontSize = 14.sp
+                )
+            }
             Spacer(modifier = Modifier.height(12.dp))
             AnimatedGif(
                 modifier = Modifier