feat: implement server-requested file re-upload via request-upload property

[Copilot]

Description

Implements support for the http://nextcloud.org/ns:request-upload WebDAV property, allowing the server to trigger client-side file re-uploads without local changes.

Changes

Core Implementation:

• Added requestUpload field to RemoteInfo struct
• Extended PROPFIND queries to fetch request-upload property
• Implemented property parsing in LsColJob::propertyMapToRemoteInfo()
• Added discovery logic to trigger uploads when property is set:
  • Checks for local file existence (including VFS placeholders)
  • Sets _instruction = CSYNC_INSTRUCTION_SYNC and _direction = SyncFileItem::Up
  • Ignores directories and virtual files without local data
  • Handles both database-known files and new remote entries

Example flow:

// Server sets property in PROPFIND response:
<nc:request-upload>1</nc:request-upload>

// Client discovers during sync:
if (serverEntry.requestUpload && !serverEntry.isDirectory && localEntry.isValid()) {
    item->_instruction = CSYNC_INSTRUCTION_SYNC;
    item->_direction = SyncFileItem::Up;
}

Testing:

• Unit tests for regular files, directories, and VFS scenarios

Use Cases

Server-initiated re-uploads for data recovery, storage migration, checksum validation, or compliance requirements.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Make the desktop client reupload a given file when requested by the remote</issue_title>
<issue_description>

Feature request

1. The nextcloud server might provide a dav property {http://nextcloud.org/ns}request-upload. That property might exists, or not. We need to request it during the propfind request for the sync. Either's either 0 or 1.

2. If request-upload is one, the client should check if we have a local copy of the file (either classic mode or vfs) and if so, we should upload that copy. It should use exactly the same logic as when the watcher detects a change for a file the file system. Alternative idea: If, for whatever reason, it's to complicate/impossible to queue an upload during the discover phase, we could also consider to just modify the mtime of the local file and let the watcher take over.
   </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Make the desktop client reupload a given file when requested by the remote #9214

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