周视图翻页改为 cross-fade 动画，消除切换空白间隙

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

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

@@ -71,7 +71,12 @@ fun WeekPager(
         modifier = modifier
     ) { page ->
         val pageOffset = abs(pagerState.currentPageOffsetFraction)
-        val alpha = 1f - pageOffset.coerceIn(0f, 0.3f) / 0.3f
+        val isCurrentPage = page == pagerState.currentPage
+        val alpha = if (isCurrentPage) {
+            1f - pageOffset
+        } else {
+            pageOffset
+        }
         val weekMonday = pageToWeekMonday(page, initialWeekMonday)
         Row(
             modifier = Modifier