[stable-3.13] Display the NC assistant in the main Window

[backportbot[bot]]

Backport of #6637

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• [x] Review and resolve any conflicts
• [x] Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[nextcloud-desktop-bot]

AppImage file: nextcloud-PR-6837-236b953c754f62f7a33da036f14c79e21bfa55d8-x86_64.AppImage

To test this change/fix you can simply download above AppImage file and test it.

Please make sure to quit your existing Nextcloud app and backup your data.

[sonarqubecloud[bot]]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)
1 New Code Smells (required ≤ 0)

See analysis details on SonarCloud

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[camilasan]

Are we backporting UI changes to 3.13?

I will check with Tobias.

[camilasan]

Are we backporting UI changes to 3.13?

I think that is fine because the UI will only change if you are running the assistant. Tobias said: "As 3.14 might take a bit longer due to QT6, I am fine with 3.13.1." I am fine either way.