feat(client): use alert only for custom provider error

client/src/www/app/app.ts

@@ -220,6 +220,8 @@ export class App {
       };
     } else if (error instanceof errors.SessionConfigError) {
       toastMessage = error.message;
+    } else if (error instanceof errors.SessionProviderError) {
+      return alert(error.message);
     } else {
       const hasErrorDetails = Boolean(error.message || error.cause);
       toastMessage = this.localize('error-unexpected');

client/src/www/app/outline_server_repository/access_key_serialization.ts

@@ -40,7 +40,7 @@ function parseShadowsocksSessionConfigJson(responseBody: string): ShadowsocksSes
   const responseJson = JSON.parse(responseBody);
 
   if ('error' in responseJson) {
-    throw new errors.SessionConfigError(responseJson.error.message);
+    throw new errors.SessionProviderError(responseJson.error.message);
   }
 
   const {method, password, server, server_port, prefix} = responseJson;

client/src/www/model/errors.ts

@@ -51,6 +51,12 @@ export class SessionConfigError extends CustomError {
   }
 }
 
+export class SessionProviderError extends CustomError {
+  constructor(message: string) {
+    super(message);
+  }
+}
+
 export class ServerAccessKeyInvalid extends CustomError {
   constructor(message: string, options?: {cause?: Error}) {
     super(message, options);