[SandObserver]

Summary

• Add folderRowZone to admin-drag-logic.js, splitting a folder row into an above/into/below zone with a quarter-height edge at each end.
• Use it in the dragover handler and in the touch place handler, so an edge zone shows drag-above/drag-below instead of drag-into.
• Track the hovered zone in both drop paths and pass targetIsFolder only when the pointer is in the middle zone.

Testing
All green. Added 3 frontend tests for the zone split and for a reordering drop on a folder row.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.
• CHANGELOG.md updated under Unreleased if the change is user-visible.