feat: add default scheme to local manager.

app/lib/models/local_schemes.dart

@@ -1,7 +1,7 @@
-export 'local_schemes_web.dart' if (dart.library.io) 'local_schemes_linux.dart';
-
 import 'package:dde_gesture_manager/models/scheme.dart';
 
+export 'local_schemes_web.dart' if (dart.library.io) 'local_schemes_linux.dart';
+
 abstract class LocalSchemeEntry {
   Scheme scheme;
   DateTime lastModifyTime;
@@ -13,6 +13,13 @@ abstract class LocalSchemeEntry {
     required this.lastModifyTime,
   });
 
+  LocalSchemeEntry.systemDefault()
+      : this.path = '',
+        this.scheme = Scheme.systemDefault(),
+
+        /// max value of DateTime ![Time Values and Time Range](https://262.ecma-international.org/11.0/#sec-time-values-and-time-range)
+        this.lastModifyTime = DateTime.fromMillisecondsSinceEpoch(8640000000000000);
+
   save();
 }
 

app/lib/models/local_schemes_linux.dart

@@ -13,7 +13,7 @@ export 'local_schemes.dart';
 @ProviderModel()
 class LocalSchemes implements LocalSchemesInterface<LocalSchemeEntryLinux> {
   LocalSchemes() {
-    schemeEntries.then((value) => schemes = value);
+    schemeEntries.then((value) => schemes = [LocalSchemeEntryLinux.systemDefault(), ...value]);
   }
 
   @override
@@ -60,6 +60,13 @@ class LocalSchemeEntryLinux implements LocalSchemeEntry {
     required this.lastModifyTime,
   });
 
+  LocalSchemeEntryLinux.systemDefault()
+      : this.path = '',
+        this.scheme = Scheme.systemDefault(),
+
+        /// max value of DateTime ![Time Values and Time Range](https://262.ecma-international.org/11.0/#sec-time-values-and-time-range)
+        this.lastModifyTime = DateTime.fromMillisecondsSinceEpoch(8640000000000000);
+
   @override
   save() {
     // TODO: implement save

app/lib/models/local_schemes_web.dart

@@ -1,17 +1,18 @@
 import 'dart:convert';
-
-import 'package:dde_gesture_manager/builder/provider_annotation.dart';
-import 'package:dde_gesture_manager/models/scheme.dart';
-import 'package:dde_gesture_manager/extensions.dart';
 import 'dart:html';
 
+import 'package:dde_gesture_manager/builder/provider_annotation.dart';
+import 'package:dde_gesture_manager/extensions.dart';
+import 'package:dde_gesture_manager/models/scheme.dart';
+
 import 'local_schemes.dart';
+
 export 'local_schemes.dart';
 
 @ProviderModel()
 class LocalSchemes implements LocalSchemesInterface<LocalSchemeEntryWeb> {
   LocalSchemes() {
-    schemeEntries.then((value) => schemes = value);
+    schemeEntries.then((value) => schemes = [LocalSchemeEntryWeb.systemDefault(), ...value]);
   }
 
   @override
@@ -59,6 +60,13 @@ class LocalSchemeEntryWeb implements LocalSchemeEntry {
     required this.lastModifyTime,
   });
 
+  LocalSchemeEntryWeb.systemDefault()
+      : this.path = '',
+        this.scheme = Scheme.systemDefault(),
+
+        /// max value of DateTime ![Time Values and Time Range](https://262.ecma-international.org/11.0/#sec-time-values-and-time-range)
+        this.lastModifyTime = DateTime.fromMillisecondsSinceEpoch(8640000000000000);
+
   @override
   save() {
     // TODO: implement save

app/lib/models/scheme.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 
 import 'package:dde_gesture_manager/builder/provider_annotation.dart';
+import 'package:dde_gesture_manager/extensions.dart';
 import 'package:dde_gesture_manager/utils/helper.dart';
 
 @ProviderModel(copyable: true)
@@ -21,6 +22,12 @@ class Scheme {
     description = scheme['desc'];
     gestures = (scheme['gestures'] as List? ?? []).map<GestureProp>((ele) => GestureProp.parse(ele)).toList();
   }
+
+  Scheme.systemDefault() {
+    this.name = LocaleKeys.local_manager_default_scheme_label.tr();
+    this.description = LocaleKeys.local_manager_default_scheme_description.tr();
+    this.gestures = [];
+  }
 }
 
 enum Gesture {