Add card gap spacing and header horizontal padding

Include CARD_GAP_DP in calendar area height calculation so BottomCard
positioning accounts for the gap. Add horizontal padding to MonthHeader
for better visual alignment.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -61,6 +61,7 @@ fun CalendarMonthView(
     val p = viewModel.collapseProgress
     val headerHeightPx = monthHeaderHeightPx + weekdayHeaderHeightPx
     val rowPaddingPx = with(density) { ROW_PADDING_DP.dp.toPx() }.toInt()
+    val cardGapPx = with(density) { CARD_GAP_DP.dp.toPx() }.toInt()
 
     val interpolatedWeeks by remember {
         derivedStateOf {
@@ -102,7 +103,7 @@ fun CalendarMonthView(
         }
     } else 0
 
-    val calendarAreaHeightPx = headerHeightPx + gridHeightPx + rowPaddingPx
+    val calendarAreaHeightPx = headerHeightPx + gridHeightPx + rowPaddingPx + cardGapPx
     val cardHeightPx = if (screenHeightPx > 0 && calendarAreaHeightPx > 0) screenHeightPx - calendarAreaHeightPx else 0
 
     // 当 rowHeightPx 已知时，用计算的高度约束 pager；否则让 pager 自由扩展以测量行高

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

@@ -24,6 +24,9 @@ const val HORIZONTAL_PADDING_DP = 16
 /** BottomCard 拖拽手势范围 (dp) */
 const val DRAG_RANGE_DP = 200
 
+/** 日历与 BottomCard 之间的间距 (dp) */
+const val CARD_GAP_DP = 12
+
 /** 线性插值 */
 fun lerp(start: Float, end: Float, fraction: Float): Float = start + (end - start) * fraction
 

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

@@ -30,7 +30,7 @@ fun MonthHeader(
     Row(
         modifier = modifier
             .fillMaxWidth()
-            .padding(vertical = 14.dp),
+            .padding(vertical = 14.dp, horizontal = 12.dp),
         verticalAlignment = Alignment.CenterVertically
     ) {
         Text(