Dense date labels: rule + label above column, row alignment Bottom

Date label cells show 'Jul 28 ────' above the thumbnail.
Cells without a label have no spacer — they sit tightly against the
row above. Row uses Alignment.Bottom so all thumbnails in a row
align at the bottom edge even when some cells have a label header
pushing them down.

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

@@ -119,6 +119,7 @@ fun DensePhotoGrid(
                 Row(
                     modifier = Modifier.fillMaxWidth().padding(horizontal = 8.dp),
                     horizontalArrangement = Arrangement.spacedBy(2.dp),
+                    verticalAlignment = Alignment.Bottom,
                 ) {
                     row.photos.forEach { labeled ->
                         DenseThumb(
@@ -171,18 +172,29 @@ private fun DenseThumb(
     }
 
     Column(modifier = modifier) {
-        // Date label or invisible spacer — keeps all thumbnails in the row aligned
         if (dateLabel != null) {
+            // Date label with trailing rule — sits above this specific column
+            Row(
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(4.dp),
+                modifier = Modifier.fillMaxWidth().padding(top = 6.dp, bottom = 2.dp),
+            ) {
                 Text(
                     dateLabel,
                     fontSize = 10.sp,
                     fontWeight = FontWeight.Medium,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
-                modifier = Modifier.height(16.dp).padding(start = 1.dp),
                 )
-        } else {
-            Spacer(Modifier.height(16.dp))
+                HorizontalDivider(
+                    modifier = Modifier.weight(1f),
+                    thickness = 0.5.dp,
+                    color = MaterialTheme.colorScheme.outlineVariant,
+                )
             }
+        }
+        // No spacer for cells without a label — rows collapse tightly.
+        // Alignment within a row is handled by the Row using Alignment.Bottom
+        // so thumbnails sit flush even when some cells have a label header.
 
         Box(
             modifier = Modifier