Share intent from third-party apps fails on Android 16 / One UI 8 / Knox 3.12 (F-Droid & Play Store version)

### ⚠️ Before posting ⚠️

- [x] This is a **bug**, not a question or an enhancement.
- [x] I've [searched for similar issues](https://github.com/nextcloud/android/issues) and didn't find a duplicate.
- [x] I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Steps to reproduce

1. Install latest Nextcloud app from F-Droid (after uninstalling Play Store version).
2. Grant all permissions: Access to all files (enabled via Settings > Privacy > Special app access), photos/videos, notifications, battery optimization disabled.
3. From any third-party app (e.g. Gallery, browser), tap Share > select Nextcloud.
4. Nothing happens: no upload dialog, no error message, share sheet closes silently.

Direct uploads via Nextcloud file picker work fine. Auto-upload also functional.

### Expected behaviour

Share intent should open Nextcloud upload dialog, allowing selection of target folder and immediate upload.

### Actual behaviour

Upload failure. No Internet connection.

### Android version

16

### Device brand and model

Samsung (One UI 8, Knox 3.12)

### Stock or custom OS?

Stock

### Nextcloud android app version

3.34.1

### Nextcloud server version

32.0.1

### Using a reverse proxy?

Yes

### Android logs

_No response_

### Server error logs

```bash

```

### Additional information

### Installation method
- F-Droid (latest version as of Nov 27, 2025)
- Previously tried Play Store version (same issue)

### Additional context
- Scoped Storage fully permitted, SAF paths configured.
- Works perfectly on iOS device with same Nextcloud server.
- Manual file browsing/upload within Nextcloud app succeeds.
- Tried: cache clear, reinstall, path changes (/storage/emulated/0/), Knox tweaks.

This blocks core share-to-cloud workflow. F-Droid was recommended as Play Store workaround due to Google permission revocation, but issue persists on Android 16 + Samsung Knox stack. [web:49][web:61]

**Related issues:** #3301, #15109 (Android 16), #14895 (F-Droid signature)