feat: FAB 菜单添加"显示调休"切换，修复个人排班标记样式

- CalendarViewModel 新增 toggleShowLegalHoliday() 方法
- FAB 菜单新增"显示调休"选项，选中高亮反馈开关状态
- DayCell 修复 showLegalHoliday=true 时个人排班标记样式：
  从"浅色背景+浅色文字"改为"accent 色实心胶囊+白色文字"
  默认模式（showLegalHoliday=false）恢复为无背景、直接浮于单元格

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

core/src/main/kotlin/plus/rua/project/CalendarViewModel.kt

@@ -186,6 +186,13 @@ class CalendarViewModel(
         }
     }
 
+    /**
+     * 切换法定调休角标显示。
+     */
+    fun toggleShowLegalHoliday() {
+        _showLegalHoliday.value = !_showLegalHoliday.value
+    }
+
     /**
      * 从年视图选择月份后返回月视图。
      */

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

@@ -388,6 +388,19 @@ fun CalendarMonthView(
                         color = MaterialTheme.colorScheme.outlineVariant,
                         modifier = Modifier.padding(horizontal = 8.dp)
                     )
+                    MenuItem(
+                        text = "显示调休",
+                        selected = showLegalHoliday,
+                        onClick = {
+                            isMenuExpanded = false
+                            viewModel.toggleShowLegalHoliday()
+                        }
+                    )
+                    HorizontalDivider(
+                        thickness = 1.dp,
+                        color = MaterialTheme.colorScheme.outlineVariant,
+                        modifier = Modifier.padding(horizontal = 8.dp)
+                    )
                     MenuItem(
                         text = "关于",
                         selected = false,

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

@@ -13,6 +13,7 @@ import androidx.compose.foundation.layout.aspectRatio
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
@@ -244,6 +245,12 @@ fun DayCell(
             } else {
                 Modifier.padding(top = 1.dp, end = 2.dp)
             }
+            val shiftBackground = if (showLegalHoliday) {
+                Modifier.background(
+                    shiftAccentColor.copy(alpha = shiftAlpha),
+                    RoundedCornerShape(4.dp)
+                )
+            } else Modifier
             Text(
                 text = shiftLabel,
                 color = shiftFgColor.copy(alpha = shiftAlpha),
@@ -253,9 +260,9 @@ fun DayCell(
                 modifier = Modifier
                     .align(shiftAlignment)
                     .zIndex(1f)
-                    .background(MaterialTheme.colorScheme.background)
+                    .then(shiftBackground)
                     .then(shiftPadding)
-                    .padding(horizontal = 2.dp)
+                    .padding(horizontal = 3.dp, vertical = 1.dp)
             )
         }
         if (showLegalHoliday && holidayBadge != null) {