Add year view with Hero Zoom transition

- CalendarViewModel: add isYearView, yearViewProgress, yearViewYear state
  with toggleYearView(), selectMonthFromYearView(), year navigation methods
- YearGridView: new 4x3 month grid with year navigation header
- MonthHeader: onClick now toggles year view, added "今天" button
- CalendarMonthView: overlay year view with graphicsLayer anchor-based
  scale transition, hide BottomCard during year view

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

@@ -0,0 +1,154 @@
+package plus.rua.project.ui
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.draw.drawBehind
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+
+/**
+ * 年度网格视图，显示 4×3 月份网格，支持年份切换。
+ *
+ * @param year 显示的年份
+ * @param selectedMonth 当前选中月份（1-12）
+ * @param onMonthClick 月份点击回调
+ * @param onYearChange 年份切换回调
+ * @param modifier 外部布局修饰符
+ */
+@Composable
+fun YearGridView(
+    year: Int,
+    selectedMonth: Int,
+    onMonthClick: (Int) -> Unit,
+    onYearChange: (Int) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    Column(
+        modifier = modifier.fillMaxSize(),
+        horizontalAlignment = Alignment.CenterHorizontally
+    ) {
+        // 年份导航行
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(vertical = 8.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Text(
+                text = "‹",
+                fontSize = 24.sp,
+                fontWeight = FontWeight.Bold,
+                color = MaterialTheme.colorScheme.primary,
+                modifier = Modifier
+                    .clip(CircleShape)
+                    .clickable { onYearChange(year - 1) }
+                    .padding(horizontal = 16.dp, vertical = 8.dp)
+            )
+            Spacer(modifier = Modifier.weight(1f))
+            Text(
+                text = "${year}年",
+                style = MaterialTheme.typography.titleLarge,
+                fontWeight = FontWeight.Bold
+            )
+            Spacer(modifier = Modifier.weight(1f))
+            Text(
+                text = "›",
+                fontSize = 24.sp,
+                fontWeight = FontWeight.Bold,
+                color = MaterialTheme.colorScheme.primary,
+                modifier = Modifier
+                    .clip(CircleShape)
+                    .clickable { onYearChange(year + 1) }
+                    .padding(horizontal = 16.dp, vertical = 8.dp)
+            )
+        }
+
+        // 4×3 月份网格
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .weight(1f)
+                .padding(horizontal = 16.dp),
+            verticalArrangement = Arrangement.SpaceEvenly
+        ) {
+            (0 until 4).forEach { row ->
+                Row(
+                    modifier = Modifier.fillMaxWidth(),
+                    horizontalArrangement = Arrangement.SpaceEvenly
+                ) {
+                    (0 until 3).forEach { col ->
+                        val month = row * 3 + col + 1
+                        MonthCell(
+                            month = month,
+                            isSelected = month == selectedMonth,
+                            onClick = { onMonthClick(month) },
+                            modifier = Modifier.weight(1f)
+                        )
+                    }
+                }
+            }
+        }
+    }
+}
+
+/**
+ * 年视图中的月份单元格。
+ */
+@Composable
+private fun MonthCell(
+    month: Int,
+    isSelected: Boolean,
+    onClick: () -> Unit,
+    modifier: Modifier = Modifier
+) {
+    val contentColor = if (isSelected) {
+        MaterialTheme.colorScheme.onPrimary
+    } else {
+        MaterialTheme.colorScheme.onSurface
+    }
+    val bgColor = MaterialTheme.colorScheme.primary
+
+    Box(
+        modifier = modifier
+            .aspectRatio(1f)
+            .padding(6.dp)
+            .clip(CircleShape)
+            .drawBehind {
+                if (isSelected) {
+                    drawCircle(
+                        color = bgColor,
+                        radius = size.minDimension / 2f,
+                        center = Offset(size.width / 2f, size.height / 2f)
+                    )
+                }
+            }
+            .clickable(onClick = onClick),
+        contentAlignment = Alignment.Center
+    ) {
+        Text(
+            text = "${month}月",
+            color = contentColor,
+            fontSize = 16.sp,
+            fontWeight = if (isSelected) FontWeight.Bold else FontWeight.Normal,
+            textAlign = TextAlign.Center
+        )
+    }
+}