perf: WeekRow 改用 graphicsLayer 避免折叠动画重组

将 offset() + alpha() 替换为 graphicsLayer { translationY / alpha }，
collapseProgress 变化时跳过 Composition/Layout，仅更新 Draw 阶段。

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

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

@@ -15,8 +15,7 @@ import androidx.compose.runtime.produceState
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clipToBounds
-import androidx.compose.ui.draw.alpha
-import androidx.compose.foundation.layout.offset
+import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.unit.dp
@@ -209,8 +208,10 @@ private fun WeekRow(
                     if (isAnchor && phase1 >= 1f) Modifier.background(MaterialTheme.colorScheme.surface)
                     else Modifier
                 )
-                .offset(y = with(density) { yOffsetPx.toDp() })
-                .alpha(rowAlpha)
+                .graphicsLayer {
+                    translationY = yOffsetPx
+                    this.alpha = rowAlpha
+                }
                 .then(
                     if (weekIndex == 0 && rowHeightPx == 0) {
                         Modifier.onSizeChanged { size ->