Arrow keys now navigate the full virtual row list (../, subdirs, patches)
rather than only patch rows. Landing on a patch auto-loads it as before;
landing on .. or a subdir highlights it and Enter confirms navigation.
Added patchVCursor to UIState to track keyboard focus independently of
the loaded patch. Mouse-click on a patch now also syncs the cursor so
subsequent arrow-key movement starts from the right position.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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