feat(desktop): improve snackbar behavior

lib/utils/snackbar_helper.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import 'layout_constants.dart';
+import 'platform_detector.dart';
 
 /// Global key for the root ScaffoldMessenger, allowing snackbars to survive navigation.
 final rootScaffoldMessengerKey = GlobalKey<ScaffoldMessengerState>();
@@ -12,19 +13,82 @@ final mainScaffoldMessengerKey = GlobalKey<ScaffoldMessengerState>();
 /// Types of snackbars available in the app
 enum SnackBarType { info, success, error }
 
+const double _kDesktopSnackBarMaxWidth = 480.0;
+const double _kDesktopSnackBarHorizontalInset = 16.0;
+const EdgeInsets _kDismissibleSnackBarPadding = EdgeInsets.symmetric(horizontal: 16, vertical: 14);
+
 /// Utility functions for showing snackbars throughout the application
 
-void showSnackBar(BuildContext context, String message, {SnackBarType type = SnackBarType.info, Duration? duration}) {
+SnackBar _buildSnackBar(
+  BuildContext context,
+  ScaffoldMessengerState messenger, {
+  required Widget content,
+  required Color? backgroundColor,
+  required Duration duration,
+  bool? dismissible,
+}) {
+  final isDesktop = PlatformDetector.isDesktopOS();
+  final tapToDismiss = dismissible ?? isDesktop;
+  final body = tapToDismiss
+      ? MouseRegion(
+          cursor: SystemMouseCursors.click,
+          child: GestureDetector(
+            behavior: HitTestBehavior.opaque,
+            onTap: () => messenger.hideCurrentSnackBar(reason: SnackBarClosedReason.dismiss),
+            child: Padding(padding: _kDismissibleSnackBarPadding, child: content),
+          ),
+        )
+      : content;
+
+  return SnackBar(
+    content: body,
+    backgroundColor: backgroundColor,
+    duration: duration,
+    behavior: isDesktop ? SnackBarBehavior.floating : null,
+    width: isDesktop ? _desktopSnackBarWidth(context) : null,
+    padding: tapToDismiss ? EdgeInsets.zero : null,
+  );
+}
+
+double _desktopSnackBarWidth(BuildContext context) {
+  final windowWidth = MediaQuery.maybeSizeOf(context)?.width;
+  if (windowWidth == null) return _kDesktopSnackBarMaxWidth;
+
+  final insetPadding = SnackBarTheme.of(context).insetPadding;
+  final horizontalInset = insetPadding == null
+      ? _kDesktopSnackBarHorizontalInset * 2
+      : insetPadding.left + insetPadding.right;
+  final availableWidth = windowWidth - horizontalInset;
+  final width = availableWidth > 0 ? availableWidth : windowWidth;
+  return width < _kDesktopSnackBarMaxWidth ? width : _kDesktopSnackBarMaxWidth;
+}
+
+(Color?, Duration) _snackBarStyle(SnackBarType type) => switch (type) {
+  SnackBarType.info => (null, AppDurations.snackBarDefault),
+  SnackBarType.success => (Colors.green, AppDurations.snackBarDefault),
+  SnackBarType.error => (Colors.red, AppDurations.snackBarLong),
+};
+
+void showSnackBar(
+  BuildContext context,
+  String message, {
+  SnackBarType type = SnackBarType.info,
+  Duration? duration,
+  bool? dismissible,
+}) {
   if (!context.mounted) return;
 
-  final (backgroundColor, defaultDuration) = switch (type) {
-    SnackBarType.info => (null, AppDurations.snackBarDefault),
-    SnackBarType.success => (Colors.green, AppDurations.snackBarDefault),
-    SnackBarType.error => (Colors.red, AppDurations.snackBarLong),
-  };
-
-  ScaffoldMessenger.of(context).showSnackBar(
-    SnackBar(content: Text(message), backgroundColor: backgroundColor, duration: duration ?? defaultDuration),
+  final (backgroundColor, defaultDuration) = _snackBarStyle(type);
+  final messenger = ScaffoldMessenger.of(context);
+  messenger.showSnackBar(
+    _buildSnackBar(
+      context,
+      messenger,
+      content: Text(message),
+      backgroundColor: backgroundColor,
+      duration: duration ?? defaultDuration,
+      dismissible: dismissible,
+    ),
   );
 }
 
@@ -38,8 +102,16 @@ void showErrorSnackBar(BuildContext context, String message) {
 
 /// Shows an error snackbar using the root ScaffoldMessenger (survives navigation).
 void showGlobalErrorSnackBar(String message) {
-  rootScaffoldMessengerKey.currentState?.showSnackBar(
-    SnackBar(content: Text(message), backgroundColor: Colors.red, duration: AppDurations.snackBarLong),
+  final messenger = rootScaffoldMessengerKey.currentState;
+  if (messenger == null) return;
+  messenger.showSnackBar(
+    _buildSnackBar(
+      messenger.context,
+      messenger,
+      content: Text(message),
+      backgroundColor: Colors.red,
+      duration: AppDurations.snackBarLong,
+    ),
   );
 }
 
@@ -48,9 +120,12 @@ void showGlobalErrorSnackBar(String message) {
 /// messenger when the main screen is not mounted.
 void showMainSnackBar(String message, {Duration duration = AppDurations.snackBarDefault}) {
   final messenger = mainScaffoldMessengerKey.currentState ?? rootScaffoldMessengerKey.currentState;
+  if (messenger == null) return;
   messenger
-    ?..removeCurrentSnackBar()
-    ..showSnackBar(SnackBar(content: Text(message), duration: duration));
+    ..removeCurrentSnackBar()
+    ..showSnackBar(
+      _buildSnackBar(messenger.context, messenger, content: Text(message), backgroundColor: null, duration: duration),
+    );
 }
 
 void showSuccessSnackBar(BuildContext context, String message) {