bug: UpdateApp cannot clear webhook_url or description once set

[deannos]

Description

UpdateApp only adds a field to the update map when the request value is non-empty:

if req.WebhookURL != "" {
    updates["webhook_url"] = req.WebhookURL
}

This means a user can never remove a previously configured webhook URL or clear a description — sending an empty string is silently ignored.

Location

handlers/app_handler.go:98–108

Fix

Use pointer fields (*string) in updateAppRequest so that null (absent) can be distinguished from "" (explicitly cleared).