Redmine

Registering a third-party OAuth2 application requires filling in the name, redirect URIs, and toggling many scope checkboxes by hand — easy to get wrong.

This patch adds an import button to the new/edit application page. A third party can distribute its config as an RFC 7591(https://www.rfc-editor.org/rfc/rfc7591) client metadata JSON file; the admin selects it and the form is prefilled. The file is parsed in the browser only.

Applied fields: `client_name` → name, `redirect_uris` → redirect URI field, `scope` → scope checkboxes (full replacement; public permissions untouched).
Unknown scopes are ignored with a warning; invalid JSON shows an error.

Sample JSON is below.

{
  "client_name": "My Issue Sync Tool",
  "redirect_uris": ["https://example.com/oauth/callback"],
  "scope": "view_issues add_issues" 
}