A plain click (press+release with no motion) left a highlighted
1-cell selection active and could claim the primary selection for a
non-blank cell, contrary to set_primary_selection_from_drag's own
doc comment. Clear selection.active on release when cur never
diverged from anchor.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KpDBFeBQKx9f5U3pfVeVV3