refactor: deduplicate

lib/utils/duration_formatter.dart

@@ -63,6 +63,15 @@ String formatDurationTimestamp(Duration duration) {
   }
 }
 
+/// Formats a sync offset in milliseconds with sign indicator (e.g., "+150ms", "-250ms").
+/// This format is used for audio/subtitle synchronization adjustments.
+///
+/// Used for: audio sync sheet, sync offset controls.
+String formatSyncOffset(double offsetMs) {
+  final sign = offsetMs >= 0 ? '+' : '';
+  return '$sign${offsetMs.round()}ms';
+}
+
 /// Gets the duration package locale based on the current app locale.
 /// Falls back to English if the locale is not supported by the duration package.
 DurationLocale _getDurationLocale() {

lib/utils/grid_cross_axis_extent.dart

@@ -0,0 +1,51 @@
+import 'package:flutter/material.dart';
+import '../services/settings_service.dart';
+
+/// Calculates the max cross-axis extent for grid items, accounting for outer padding.
+double getMaxCrossAxisExtentWithPadding(
+  BuildContext context,
+  LibraryDensity density,
+  double horizontalPadding,
+) {
+  final screenWidth = MediaQuery.of(context).size.width;
+  final availableWidth = screenWidth - horizontalPadding;
+
+  if (screenWidth >= 900) {
+    // Wide screens (desktop/large tablet landscape): Responsive division
+    double divisor;
+    double maxItemWidth;
+
+    switch (density) {
+      case LibraryDensity.comfortable:
+        divisor = 6.5;
+        maxItemWidth = 280;
+        break;
+      case LibraryDensity.normal:
+        divisor = 8.0;
+        maxItemWidth = 200;
+        break;
+      case LibraryDensity.compact:
+        divisor = 10.0;
+        maxItemWidth = 160;
+        break;
+    }
+
+    return (availableWidth / divisor).clamp(0, maxItemWidth);
+  } else if (screenWidth >= 600) {
+    // Medium screens (tablets): Fixed 4-5-6 items
+    int targetItemCount = switch (density) {
+      LibraryDensity.comfortable => 4,
+      LibraryDensity.normal => 5,
+      LibraryDensity.compact => 6,
+    };
+    return availableWidth / targetItemCount;
+  } else {
+    // Small screens (phones): Fixed 2-3-4 items
+    int targetItemCount = switch (density) {
+      LibraryDensity.comfortable => 2,
+      LibraryDensity.normal => 3,
+      LibraryDensity.compact => 4,
+    };
+    return availableWidth / targetItemCount;
+  }
+}