Remind users to use QGIS plugin to download projects that they plan to edit

Summary

As a QGIS user, I want a reminder of the correct way to download a project to work on in QGIS, so that I don't make edits that I cannot synchronise back to the server.

Description

I have a suggestion for a website UI change.

Some of our users have been unable to sync projects from their laptops via QGIS.  The reason was that they had downloaded the project directly from the server via their web browser, rather than using the Mergin Maps plugin tool in the QGIS Browser panel.  Downloading directly from the website doesn't register the project within QGIS and leaves the sync button disabled.

We did show them how to use the QGIS plugin tool, but still they go to the website.  I think it's because the Mergin Maps button on the QGIS plugin takes them there.  If the web browser has cached the password, then you immediately see the projects and it seems natural to click one and download it.

One way to avoid this is to show a popup after a user presses the Download button that says something like:

Press "OK" to download a standalone snapshot of my_project (version 123). If you plan to edit data in QGIS and synchronise changes, please use the Mergin Maps QGIS plugin to download the project instead.

An alternative would be to modify the QGIS plugin so that clicking the website button displays a QMessageBox to remind users about the Mergin Maps tool in the QGIS Browser panel before continuing to the website.

Acceptance criteria

• Users are reminded that the way to download a project for editing in QGIS is via the Mergin Maps QGIS plugin

No files or tests are named. Start by tracing the website Download action and the Mergin Maps QGIS plugin link, then determine which reminder approach fits the existing flow. Done means users are clearly told to use the QGIS plugin when downloading a project they plan to edit and synchronise.