ImportScreen: replace fade with bottom edge shadow

24dp shadow strip on the bottom edge of the scroll area when more
content is below. Disappears when scrolled to bottom. Matches how
Material dialogs and macOS sheets indicate overflow.

src/main/kotlin/com/bolenpad/photophetch/ui/ImportScreen.kt

@@ -46,11 +46,27 @@ fun ImportScreen(state: AppState) {
 
         HorizontalDivider()
 
-        // ── Scrollable body with bottom fade ────────────────────────────────
+        // ── Scrollable body with bottom shadow indicator ─────────────────────
         val scrollState = rememberScrollState()
-        val showFade by remember { derivedStateOf { scrollState.value < scrollState.maxValue } }
+        val showShadow by remember { derivedStateOf { scrollState.value < scrollState.maxValue } }
 
-        Box(modifier = Modifier.weight(1f)) {
+        Box(
+            modifier = Modifier
+                .weight(1f)
+                .then(
+                    if (showShadow) Modifier.drawWithContent {
+                        drawContent()
+                        // Thin shadow strip along the bottom edge
+                        drawRect(
+                            brush = Brush.verticalGradient(
+                                colors = listOf(Color.Transparent, Color.Black.copy(alpha = 0.10f)),
+                                startY = size.height - 24.dp.toPx(),
+                                endY = size.height,
+                            )
+                        )
+                    } else Modifier
+                )
+        ) {
             Column(
                 modifier = Modifier
                     .fillMaxSize()
@@ -142,26 +158,6 @@ fun ImportScreen(state: AppState) {
             // Extra bottom padding so last item isn't flush against the button
             Spacer(Modifier.height(8.dp))
         } // end scroll Column
-
-        // Fade gradient — visible when not scrolled to bottom
-        if (showFade) {
-            Box(
-                modifier = Modifier
-                    .fillMaxWidth()
-                    .height(48.dp)
-                    .align(Alignment.BottomCenter)
-                    .drawWithContent {
-                        drawContent()
-                        drawRect(
-                            brush = Brush.verticalGradient(
-                                colors = listOf(Color.Transparent, Color.White),
-                                startY = 0f,
-                                endY = size.height,
-                            )
-                        )
-                    }
-            )
-        }
         } // end Box
 
         // ── Pinned bottom button ─────────────────────────────────────────────