Fix week number alignment: use Bottom + padding instead of alignByBaseline

alignByBaseline caused layout jumps during AnimatedContent transitions.
Switch to Bottom alignment with 2dp bottom padding on week number for
stable visual alignment with month text baseline.

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

@@ -41,7 +41,7 @@ fun MonthHeader(
             .fillMaxWidth()
             .padding(vertical = 14.dp, horizontal = 12.dp)
             .then(if (onClick != null) Modifier.clickable(onClick = onClick) else Modifier),
-        verticalAlignment = Alignment.CenterVertically
+        verticalAlignment = Alignment.Bottom
     ) {
         AnimatedContent(
             targetState = Pair(year, month),
@@ -53,8 +53,7 @@ fun MonthHeader(
                     slideInVertically(tween(250)) { it } + fadeIn(tween(250)) togetherWith
                             slideOutVertically(tween(250)) { -it } + fadeOut(tween(250))
                 }
-            },
-            modifier = Modifier.alignByBaseline()
+            }
         ) { (y, m) ->
             Text(
                 text = "${y}年${m}月",
@@ -73,7 +72,7 @@ fun MonthHeader(
                             slideOutVertically(tween(250)) { -it } + fadeOut(tween(250))
                 }
             },
-            modifier = Modifier.alignByBaseline()
+            modifier = Modifier.padding(bottom = 2.dp)
         ) { week ->
             Text(
                 text = "第${week}周",