Allow configuring or batching the 500-file upload limit in the Nextcloud mobile app

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**Is your feature request related to a problem? Please describe.**
The Nextcloud mobile app currently limits uploads to 500 files at a time, showing this message:
> “You have reached the maximum file upload limit. Please upload fewer than 500 files at a time.”

This restriction blocks the auto-upload feature when a source folder (like a phone’s camera roll) contains more than 500 photos. In these cases, the app refuses to upload *any* files at all.

For users with large media folders, like people initially downloading the app to use auto upload to backup a long gallery history, this becomes a significant barrier and forces manual workarounds.

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**Describe the solution you'd like**
Make the 500-file upload limit configurable in the app settings or batch uploads automatically when a folder exceeds that number.
Possible implementations:
- Add a configurable “Maximum files per batch” option in the Auto Upload settings (default 500).
- Alternatively, automatically process uploads in multiple batches of 500 files until the full folder is uploaded.

Or both?

This would keep the current stability for most users while allowing advanced users or administrators to raise or remove the limit.

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**Describe alternatives you've considered**
- Manually splitting large folders into smaller ones under 500 files (inefficient and not clear for less technical users).
- Using the desktop sync client to upload large folders (defeats the purpose of mobile auto-upload).
- Rebuilding the app from source with a higher constant (impractical for normal users, loses the benefit of being easy to install from play store).

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**Additional context**
Environment: Nextcloud running on TrueNAS Scale, served via Apache behind Nginx Proxy Manager.
Server upload limits (PHP, Apache, proxy) have been verified as sufficient — the restriction occurs entirely within the mobile app.
Allowing this limit to be configurable or automatically batched would remove a usability bottleneck for users syncing large photo collections.

Basically my family take a tonne of photos and inital switch to the app is blocked by the fact they cannot get uploads to work!