Replace button-triggered collapse with vertical drag gesture

ViewModel now exposes onDrag/onDragEnd so BottomCard drives the
collapse animation via detectVerticalDragGestures instead of a
discrete collapse() call. Drag maps to 0–1 progress over 200dp;
on release the animatable snaps to the nearest end with spring.

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

shared/src/commonMain/kotlin/plus/rua/project/CalendarViewModel.kt

@@ -1,6 +1,7 @@
 package plus.rua.project
 
 import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.spring
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.setValue
@@ -42,33 +43,29 @@ class CalendarViewModel(private val coroutineScope: CoroutineScope) {
         selectedDate = date
     }
 
-    fun collapse() {
+    fun onDrag(delta: Float) {
-        if (isCollapsed) return
         coroutineScope.launch {
-            _collapseAnimatable.animateTo(
+            val new = (_collapseAnimatable.value + delta).coerceIn(0f, 1f)
-                targetValue = 1f,
+            _collapseAnimatable.snapTo(new)
-                animationSpec = androidx.compose.animation.core.spring(
-                    dampingRatio = 0.8f,
-                    stiffness = 400f
-                )
-            )
-            isCollapsed = true
         }
     }
 
-    fun expand() {
+    fun onDragEnd() {
-        if (!isCollapsed) return
-        isCollapsed = false
         coroutineScope.launch {
+            if (_collapseAnimatable.value > 0.5f) {
+                _collapseAnimatable.animateTo(
+                    targetValue = 1f,
+                    animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)
+                )
+                isCollapsed = true
+            } else {
                 _collapseAnimatable.animateTo(
                     targetValue = 0f,
-                animationSpec = androidx.compose.animation.core.spring(
+                    animationSpec = spring(dampingRatio = 0.8f, stiffness = 400f)
-                    dampingRatio = 0.8f,
-                    stiffness = 400f
-                )
                 )
             }
         }
+    }
 
     fun getIsoWeekNumber(date: LocalDate): Int {
         val jan4 = LocalDate(date.year, 1, 4)

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

@@ -1,6 +1,5 @@
 package plus.rua.project.ui
 
-import androidx.compose.animation.core.animate
 import androidx.compose.foundation.background
 import androidx.compose.foundation.gestures.detectVerticalDragGestures
 import androidx.compose.foundation.layout.Box
@@ -12,14 +11,13 @@ import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.unit.dp
-import kotlinx.coroutines.launch
 import plus.rua.project.CalendarViewModel
 
 @Composable
@@ -27,16 +25,20 @@ fun BottomCard(
     viewModel: CalendarViewModel,
     modifier: Modifier = Modifier
 ) {
-    val coroutineScope = rememberCoroutineScope()
+    val density = LocalDensity.current
+    val dragRange = with(density) { 200.dp.toPx() }
 
     Surface(
         modifier = modifier
             .fillMaxWidth()
-            .pointerInput(Unit) {
+            .pointerInput(viewModel.isCollapsed) {
-                detectVerticalDragGestures { _, dragAmount ->
+                if (viewModel.isCollapsed) return@pointerInput
-                    if (dragAmount < 0 && !viewModel.isCollapsed) {
+                detectVerticalDragGestures(
-                        viewModel.collapse()
+                    onDragEnd = { viewModel.onDragEnd() },
-                    }
+                    onDragCancel = { viewModel.onDragEnd() }
+                ) { _, dragAmount ->
+                    val delta = -dragAmount / dragRange
+                    viewModel.onDrag(delta)
                 }
             },
         shape = RoundedCornerShape(topStart = 16.dp, topEnd = 16.dp),