Fix VoiceOver labels in share extension folder picker

[web3blind]

Summary

• add an explicit accessibility label to folder cells in the share extension target-folder picker
• include the visible folder name and metadata text that is already shown in the cell
• expose folder rows as actionable elements for VoiceOver users

Issue

Fixes #4099

Testing

• Not run: iOS/Xcode build is not available in this environment
• Static inspection: verified the share extension uses NCListCell for target folders and now calls setAccessibility(label:value:) for each cell

Accessibility impact

This should let VoiceOver announce the folder name/details while sharing a file into Nextcloud from another app, instead of focusing unnamed selectable rows.