[auth] Add Appbar Lock Icon for Manual App Locking on Desktop + fix bugs (#3108)

## Description

When app lock is enabled on Auth's desktop app and when
closed/minimised, the app is not getting locked in certain cases. As a
workaround for that, have added a button to manually lock the app.

auth/lib/l10n/arb/app_en.arb

@@ -466,5 +466,7 @@
   "pinLock": "Pin lock",
   "enterPin": "Enter PIN",
   "setNewPin": "Set new PIN",
-  "importFailureDescNew": "Could not parse the selected file."
+  "importFailureDescNew": "Could not parse the selected file.",
+  "appLockNotEnabled": "App lock not enabled",
+  "appLockNotEnabledDescription": "Please enable app lock from Security > App Lock"
 }

auth/lib/ui/home_page.dart

@@ -22,11 +22,15 @@ import 'package:ente_auth/ui/account/logout_dialog.dart';
 import 'package:ente_auth/ui/code_error_widget.dart';
 import 'package:ente_auth/ui/code_widget.dart';
 import 'package:ente_auth/ui/common/loading_widget.dart';
+import 'package:ente_auth/ui/components/buttons/button_widget.dart';
+import 'package:ente_auth/ui/components/dialog_widget.dart';
+import 'package:ente_auth/ui/components/models/button_type.dart';
 import 'package:ente_auth/ui/home/coach_mark_widget.dart';
 import 'package:ente_auth/ui/home/home_empty_state.dart';
 import 'package:ente_auth/ui/home/speed_dial_label_widget.dart';
 import 'package:ente_auth/ui/scanner_page.dart';
 import 'package:ente_auth/ui/settings_page.dart';
+import 'package:ente_auth/ui/tools/app_lock.dart';
 import 'package:ente_auth/utils/dialog_util.dart';
 import 'package:ente_auth/utils/platform_util.dart';
 import 'package:ente_auth/utils/totp_util.dart';
@@ -199,6 +203,28 @@ class _HomePageState extends State<HomePage> {
     }
   }
 
+  Future<void> navigateToLockScreen() async {
+    final bool shouldShowLockScreen =
+        await Configuration.instance.shouldShowLockScreen();
+    if (shouldShowLockScreen) {
+      await AppLock.of(context)!.showLockScreen();
+    } else {
+      await showDialogWidget(
+        context: context,
+        title: context.l10n.appLockNotEnabled,
+        body: context.l10n.appLockNotEnabledDescription,
+        isDismissible: true,
+        buttons: const [
+          ButtonWidget(
+            buttonType: ButtonType.secondary,
+            labelText: "OK",
+            isInAlert: true,
+          ),
+        ],
+      );
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final l10n = context.l10n;
@@ -251,8 +277,20 @@ class _HomePageState extends State<HomePage> {
                   ),
                   focusNode: searchBoxFocusNode,
                 ),
-          centerTitle: true,
+          centerTitle: PlatformUtil.isDesktop() ? false : true,
           actions: <Widget>[
+            PlatformUtil.isDesktop()
+                ? IconButton(
+                    icon: const Icon(Icons.lock),
+                    tooltip: l10n.appLock,
+                    onPressed: () async {
+                      await navigateToLockScreen();
+                    },
+                  )
+                : const SizedBox.shrink(),
+            const SizedBox(
+              width: 4,
+            ),
             IconButton(
               icon: _showSearchBox
                   ? const Icon(Icons.clear)

auth/lib/ui/settings/lock_screen/lock_screen_options.dart

@@ -5,9 +5,12 @@ import "package:ente_auth/core/configuration.dart";
 import "package:ente_auth/l10n/l10n.dart";
 import "package:ente_auth/services/local_authentication_service.dart";
 import "package:ente_auth/theme/ente_theme.dart";
+import "package:ente_auth/ui/components/buttons/button_widget.dart";
 import "package:ente_auth/ui/components/captioned_text_widget.dart";
+import "package:ente_auth/ui/components/dialog_widget.dart";
 import "package:ente_auth/ui/components/divider_widget.dart";
 import "package:ente_auth/ui/components/menu_item_widget.dart";
+import "package:ente_auth/ui/components/models/button_type.dart";
 import "package:ente_auth/ui/components/title_bar_title_widget.dart";
 import "package:ente_auth/ui/components/title_bar_widget.dart";
 import "package:ente_auth/ui/components/toggle_switch_widget.dart";
@@ -15,7 +18,6 @@ import "package:ente_auth/ui/settings/lock_screen/lock_screen_auto_lock.dart";
 import "package:ente_auth/ui/settings/lock_screen/lock_screen_password.dart";
 import "package:ente_auth/ui/settings/lock_screen/lock_screen_pin.dart";
 import "package:ente_auth/ui/tools/app_lock.dart";
-import "package:ente_auth/utils/dialog_util.dart";
 import "package:ente_auth/utils/lock_screen_settings.dart";
 import "package:ente_auth/utils/navigation_util.dart";
 import "package:ente_auth/utils/platform_util.dart";
@@ -67,10 +69,18 @@ class _LockScreenOptionsState extends State<LockScreenOptions> {
       await _lockscreenSetting.removePinAndPassword();
       await _configuration.setSystemLockScreen(!isSystemLockEnabled);
     } else {
-      await showErrorDialog(
-        context,
-        context.l10n.noSystemLockFound,
-        context.l10n.deviceLockEnablePreSteps,
+      await showDialogWidget(
+        context: context,
+        title: context.l10n.noSystemLockFound,
+        body: context.l10n.deviceLockEnablePreSteps,
+        isDismissible: true,
+        buttons: const [
+          ButtonWidget(
+            buttonType: ButtonType.secondary,
+            labelText: "OK",
+            isInAlert: true,
+          ),
+        ],
       );
     }
     await _initializeSettings();

auth/lib/ui/tools/lock_screen.dart

@@ -1,3 +1,4 @@
+import 'dart:io';
 import 'dart:math';
 
 import 'package:ente_auth/core/configuration.dart';
@@ -193,6 +194,8 @@ class _LockScreenState extends State<LockScreen> with WidgetsBindingObserver {
       isCritical: true,
       firstButtonOnTap: () async {
         await UserService.instance.logout(context);
+        // To start the app afresh, resetting all state.
+        Process.killPid(pid, ProcessSignal.sigkill);
       },
     );
   }