spec: vertical multi-caret (Alt+Up/Down, Alt+Drag) — re-spec of PR #125#133

tig wants to merge 4 commits into

developgui-cs/Editor:developfrom

claude/spec-pr-125-reimplementation-rVWsCgui-cs/Editor:claude/spec-pr-125-reimplementation-rVWsCCopy head branch name to clipboard