feat: expose outlookSubscription in account info API

Add outlookSubscription field to GET /v1/account/{account} response
to allow users to retrieve Microsoft Graph subscription details,
including clientState for webhook validation at proxy level.

Author: andris9

lib/api-routes/account-routes.js

@@ -817,7 +817,8 @@ async function init(args) {
                     'connections',
                     'webhooksCustomHeaders',
                     'locale',
-                    'tz'
+                    'tz',
+                    'outlookSubscription'
                 ]) {
                     if (key in accountData) {
                         result[key] = accountData[key];
@@ -1014,6 +1015,17 @@ async function init(args) {
 
                     syncTime: Joi.date().iso().example('2021-02-17T13:43:18.860Z').description('Last sync time'),
 
+                    outlookSubscription: Joi.object({
+                        id: Joi.string().description('Microsoft Graph subscription ID'),
+                        expirationDateTime: Joi.date().iso().description('When the subscription expires'),
+                        clientState: Joi.string().description('Shared secret for validating webhook notifications'),
+                        state: Joi.object({
+                            state: Joi.string().valid('creating', 'created', 'error').description('Subscription state'),
+                            time: Joi.number().description('Timestamp of last state change'),
+                            error: Joi.string().description('Error message if state is error')
+                        }).description('Current subscription state')
+                    }).description('Microsoft Graph subscription details (Outlook accounts only)'),
+
                     lastError: lastErrorSchema.allow(null)
                 }).label('AccountResponse'),
                 failAction: 'log'