feat: enhance error handling in Stalwart API responses

locales/en/common.json

@@ -993,7 +993,7 @@
       "title": "Account Security",
       "description": "Manage your password, two-factor authentication, and security settings",
       "detecting": "Detecting server capabilities...",
-      "not_available": "Account security management is not available for this mail server.",
+      "not_available": "Account security management is not available for this mail server. Required permissions may be disabled. See the <a href=\"/docs/guides/account-security\" class=\"underline hover:opacity-80\" target=\"_blank\">documentation</a> for details.",
       "password": {
         "title": "Change Password",
         "current": "Current Password",
@@ -1009,6 +1009,7 @@
       "display_name": {
         "label": "Display Name",
         "description": "Your name as it appears on the server",
+        "placeholder": "Enter your display name",
         "save": "Save",
         "success": "Display name updated",
         "error": "Failed to update display name"