Accessibility: keyboard navigation, VoiceOver, focus management, reduced motion

[veganstraightedge]

• Keyboard navigation: Arrow keys for tree navigation (up/down to move between visible rows, left to collapse/go to parent, right to expand/go to first child). Tab to move between filter field and tree. How does this interact with the three interaction modes (normal/filter/rename)?
• VoiceOver: What does VoiceOver announce for each row? Filename, file type, source control status, open/modified state? In what order?
• Focus management: When a file is opened via Enter in filter mode, where does focus go — back to the tree, or to the document area? May depend on the host app.
• Reduced Motion: Should expand/collapse animations respect `accessibilityReduceMotion`?