refactor: 移除 fling 速度阈值，改用 spring 动画驱动折叠过渡

- ViewModel onDragEnd/onExpandDragEnd 移除 velocity 参数
- BottomCard 移除 VelocityTracker，简化回调签名
- CalendarMonthView 添加 animateFloatAsState spring 动画
- 更新单元测试：移除 fling 测试，调整阈值边界

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

core/src/main/kotlin/plus/rua/project/CalendarViewModel.kt

@@ -18,7 +18,6 @@ import kotlinx.datetime.number
 import kotlinx.datetime.plus
 import kotlinx.datetime.todayIn
 import plus.rua.project.ui.COLLAPSE_THRESHOLD
-import plus.rua.project.ui.FLING_VELOCITY_THRESHOLD_DP
 import plus.rua.project.ui.getMonthGridInfo
 import kotlin.time.Clock
 
@@ -215,25 +214,17 @@ class CalendarViewModel(
      * @param delta 拖拽增量，已归一化到 [0,1] 区间
      */
     fun onDrag(delta: Float) {
-        val new = (_collapseProgress.value + delta).coerceIn(0f, 1f)
-        _collapseProgress.value = new
+        _collapseProgress.value = (_collapseProgress.value + delta).coerceIn(0f, 1f)
     }
 
     /**
-     * 展开状态拖拽结束，根据进度和速度决定折叠或回弹。
+     * 展开状态拖拽结束，根据进度决定折叠或回弹。
      *
      * 拖拽超过阈值时自动折叠到周视图，否则回弹到月视图。
-     *
-     * @param velocityDpPerSec 松手时的 fling 速度 (dp/s)，正值=上滑（折叠方向），负值=下滑（展开方向）
      */
-    fun onDragEnd(velocityDpPerSec: Float = 0f) {
+    fun onDragEnd() {
         val progress = _collapseProgress.value
-        val shouldCollapse = when {
-            velocityDpPerSec > FLING_VELOCITY_THRESHOLD_DP -> true
-            velocityDpPerSec < -FLING_VELOCITY_THRESHOLD_DP -> false
-            else -> progress > COLLAPSE_THRESHOLD
-        }
-        if (shouldCollapse) {
+        if (progress > COLLAPSE_THRESHOLD) {
             _isCollapsed.value = true
             _collapseProgress.value = 1f
         } else {
@@ -248,25 +239,17 @@ class CalendarViewModel(
      * @param delta 拖拽增量，已归一化到 [0,1] 区间
      */
     fun onExpandDrag(delta: Float) {
-        val new = (_collapseProgress.value + delta).coerceIn(0f, 1f)
-        _collapseProgress.value = new
+        _collapseProgress.value = (_collapseProgress.value + delta).coerceIn(0f, 1f)
     }
 
     /**
-     * 折叠状态拖拽结束，根据进度和速度决定展开或回弹。
+     * 折叠状态拖拽结束，根据进度决定展开或回弹。
      *
      * 下拉超过阈值时自动展开到月视图，否则回弹到周视图。
-     *
-     * @param velocityDpPerSec 松手时的 fling 速度 (dp/s)，正值=上滑，负值=下滑
      */
-    fun onExpandDragEnd(velocityDpPerSec: Float = 0f) {
+    fun onExpandDragEnd() {
         val progress = _collapseProgress.value
-        val shouldExpand = when {
-            velocityDpPerSec < -FLING_VELOCITY_THRESHOLD_DP -> true
-            velocityDpPerSec > FLING_VELOCITY_THRESHOLD_DP -> false
-            else -> progress < COLLAPSE_THRESHOLD
-        }
-        if (shouldExpand) {
+        if (progress < (1 - COLLAPSE_THRESHOLD)) {
             _isCollapsed.value = false
             _collapseProgress.value = 0f
         } else {

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

@@ -60,13 +60,12 @@ fun BottomCard(
     today: LocalDate,
     shiftKind: ShiftKind?,
     onDrag: (Float) -> Unit,
-    onDragEnd: (Float) -> Unit,
+    onDragEnd: () -> Unit,
     onExpandDrag: (Float) -> Unit,
-    onExpandDragEnd: (Float) -> Unit,
+    onExpandDragEnd: () -> Unit,
     dragRangePx: Float,
     modifier: Modifier = Modifier
 ) {
-    val density = LocalDensity.current
     val relativeDesc = relativeDayDescription(selectedDate, today)
 
     @Suppress("DEPRECATION") // monthNumber 无替代 API，kotlinx-datetime 尚未提供新接口
@@ -87,36 +86,21 @@ fun BottomCard(
         modifier = modifier
             .fillMaxWidth()
             .pointerInput(isCollapsed) {
-                val velocityTracker = androidx.compose.ui.input.pointer.util.VelocityTracker()
                 if (isCollapsed) {
                     // 折叠状态：下拉恢复到月视图
                     detectVerticalDragGestures(
-                        onDragEnd = {
-                            val velocity = velocityTracker.calculateVelocity()
-                            val velocityDpPerSec = with(density) { -velocity.y.toDp().value }
-                            onExpandDragEnd(velocityDpPerSec)
-                        },
-                        onDragCancel = {
-                            onExpandDragEnd(0f)
-                        }
-                    ) { change, dragAmount ->
-                        velocityTracker.addPosition(change.uptimeMillis, change.position)
+                        onDragEnd = { onExpandDragEnd() },
+                        onDragCancel = { onExpandDragEnd() }
+                    ) { _, dragAmount ->
                         val delta = -dragAmount / dragRangePx
                         onExpandDrag(delta)
                     }
                 } else {
                     // 展开状态：上拉折叠到周视图
                     detectVerticalDragGestures(
-                        onDragEnd = {
-                            val velocity = velocityTracker.calculateVelocity()
-                            val velocityDpPerSec = with(density) { -velocity.y.toDp().value }
-                            onDragEnd(velocityDpPerSec)
-                        },
-                        onDragCancel = {
-                            onDragEnd(0f)
-                        }
-                    ) { change, dragAmount ->
-                        velocityTracker.addPosition(change.uptimeMillis, change.position)
+                        onDragEnd = { onDragEnd() },
+                        onDragCancel = { onDragEnd() }
+                    ) { _, dragAmount ->
                         val delta = -dragAmount / dragRangePx
                         onDrag(delta)
                     }

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

@@ -6,6 +6,9 @@ import androidx.compose.animation.EnterTransition
 import androidx.compose.animation.ExitTransition
 import androidx.compose.animation.SharedTransitionLayout
 import androidx.compose.animation.core.FastOutSlowInEasing
+import androidx.compose.animation.core.Spring
+import androidx.compose.animation.core.animateFloatAsState
+import androidx.compose.animation.core.spring
 import androidx.compose.animation.core.tween
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
@@ -107,6 +110,13 @@ fun CalendarMonthView(
     val collapseProgress = uiState.collapseProgress
     val showLegalHoliday = uiState.showLegalHoliday
 
+    // 松手后 progress 从当前值 spring 动画到目标值（0 或 1）
+    val animatedCollapseProgress by animateFloatAsState(
+        targetValue = collapseProgress,
+        animationSpec = spring(stiffness = Spring.StiffnessMedium),
+        label = "collapseProgress"
+    )
+
     val density = LocalDensity.current
     val coroutineScope = rememberCoroutineScope()
 
@@ -215,7 +225,7 @@ fun CalendarMonthView(
                                     selectedDate = selectedDate,
                                     today = today,
                                     isCollapsed = isCollapsed,
-                                    collapseProgress = collapseProgress,
+                                    collapseProgress = animatedCollapseProgress,
                                     showLegalHoliday = showLegalHoliday,
                                     rowHeightPx = rowHeightPx,
                                     screenWidthPx = screenWidthPx,
@@ -562,9 +572,9 @@ private fun BottomCardArea(
             today = today,
             shiftKind = shiftKind,
             onDrag = { delta -> viewModel.onDrag(delta) },
-            onDragEnd = { velocity -> viewModel.onDragEnd(velocity) },
+            onDragEnd = { viewModel.onDragEnd() },
             onExpandDrag = { delta -> viewModel.onExpandDrag(delta) },
-            onExpandDragEnd = { velocity -> viewModel.onExpandDragEnd(velocity) },
+            onExpandDragEnd = { viewModel.onExpandDragEnd() },
             dragRangePx = dragRangePx,
             modifier = modifier
                 .offset(y = with(density) { (slideProgress * 200).dp })

core/src/test/kotlin/plus/rua/project/CalendarViewModelStateTest.kt

@@ -311,7 +311,7 @@ class CalendarViewModelStateTest {
     fun onExpandDragEnd_progressBelowThreshold_expands() {
         val vm = createViewModel()
         vm.onDrag(1f)
-        vm.onExpandDrag(-0.95f)
+        vm.onExpandDrag(-0.15f) // progress = 0.85 < 0.92
         vm.onExpandDragEnd()
         assertFalse(vm.isCollapsed.value)
         assertEquals(0f, vm.collapseProgress.value, 0.001f)
@@ -321,50 +321,12 @@ class CalendarViewModelStateTest {
     fun onExpandDragEnd_progressAboveThreshold_staysCollapsed() {
         val vm = createViewModel()
         vm.onDrag(1f)
-        vm.onExpandDrag(-0.05f)
+        vm.onExpandDrag(-0.05f) // progress = 0.95 > 0.92
         vm.onExpandDragEnd()
         assertTrue(vm.isCollapsed.value)
         assertEquals(1f, vm.collapseProgress.value, 0.001f)
     }
 
-    @Test
-    fun onDragEnd_fastFlingUp_setsCollapsed() {
-        val vm = createViewModel()
-        vm.onDrag(0.1f)
-        vm.onDragEnd(velocityDpPerSec = 900f)
-        assertTrue(vm.isCollapsed.value)
-        assertEquals(1f, vm.collapseProgress.value, 0.001f)
-    }
-
-    @Test
-    fun onDragEnd_fastFlingDown_keepsExpanded() {
-        val vm = createViewModel()
-        vm.onDrag(0.9f)
-        vm.onDragEnd(velocityDpPerSec = -900f)
-        assertFalse(vm.isCollapsed.value)
-        assertEquals(0f, vm.collapseProgress.value, 0.001f)
-    }
-
-    @Test
-    fun onExpandDragEnd_fastFlingDown_setsExpanded() {
-        val vm = createViewModel()
-        vm.onDrag(1f)
-        vm.onExpandDrag(-0.1f)
-        vm.onExpandDragEnd(velocityDpPerSec = -900f)
-        assertFalse(vm.isCollapsed.value)
-        assertEquals(0f, vm.collapseProgress.value, 0.001f)
-    }
-
-    @Test
-    fun onExpandDragEnd_fastFlingUp_staysCollapsed() {
-        val vm = createViewModel()
-        vm.onDrag(1f)
-        vm.onExpandDrag(-0.9f)
-        vm.onExpandDragEnd(velocityDpPerSec = 900f)
-        assertTrue(vm.isCollapsed.value)
-        assertEquals(1f, vm.collapseProgress.value, 0.001f)
-    }
-
     // ---- getMonthDays 与 selectedDate 配合 ----
 
     @Test