fix: show confirm dialog on closing upload tab

[mykh-hailo]

• Resolves: [Bug]: Closing Tab stops upload without confirmation request. #52781

Summary

This PR adds a beforeunload safeguard to prevent users from accidentally closing or navigating away from the page while uploads are still active.

A new upload guard service is introduced in apps/files/src/services/UploadBeforeUnload.ts and registered in both:

• apps/files/src/main.ts (regular Files app)
• apps/files_sharing/src/init-public.ts (public sharing/file drop flow)

When the uploader status is not idle (including uploading or paused), the browser is prompted with a warning that leaving the page will cancel ongoing uploads. The listener is registered only once to avoid duplicate handlers.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[skjnldsv]

Thanks for the PR @mykh-hailo, let's discuss this

@susnux better to have this as a core uploader feature, no ?

[mykh-hailo]

@susnux Could you possibly share your idea about this PR and @skjnldsv 's comment?

[susnux]

better to have this as a core uploader feature, no ?

Yes I think this should be part of the Uploader Vue component (but not of the uploader API class).

[skjnldsv]

@mykh-hailo we use a shared component for uploading.
This is located here https://github.com/nextcloud-libraries/nextcloud-upload/tree/main/lib/vue/components

I think it should be a shared feature, so anyone using the upload component benefit from this ! 👍

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