Cannot add changed layers from Changes viewer to project ("Add to project" button missing)

Description
User is unable to add changed layers from Changes viewer to the project to inspect them further or use them to restore deleted or modified data. The button "Add to project" is not available in changes viewer.

Environment
Staging/PROD

Application (+ app version, build, operating system)

• QGIS version: 3.40.5-Bratislava
• Plugin version: 2025.2
• OS: macOS, Sequoia 15.5

Steps to reproduce

1. Go to QGIS and open a project.
2. Press history for an older project.
3. Select a version with some changes in a layer (added, updated, deleted feature).
4. Click Add to project button

Actual results
The button "Add to project" is not available in the Changes viewer, so changed layers cannot be added to the project for further inspection or restoration.

Expected results
There should be an option (button) to add changed layers from the Changes viewer to the project, allowing users to inspect or restore deleted/modified data.

See documentation: https://merginmaps.com/docs/manage/project-history/#project-history-in-qgis

Screenshots or logs
N/A

Start by reproducing the missing control in the Changes viewer using QGIS 3.40.5 and review the Project history documentation linked in the issue. Locate the Changes viewer entry point in the plugin, then verify that changed layers can be added to the open project for inspection or restoration; the issue names no files or tests.