Shell · ColumnShell: columns to the window's top, each under a header that drags it; the traffic lights or controls in the first or last (#6)

tasks/github.md

@@ -9,6 +9,6 @@
 # GitHub round, 2026-10-05
 
 - [x] G6 Issue #7: an IME composition restarts the caret's blink, as every edit does; its ranges are logged; tested
-- [ ] G7 Issue #6: `layout::SidebarShell`, a sidebar that runs to the window's top with the traffic lights, beside one or two panes that bring their own headers; tested
+- [x] G7 Issue #6: `shell::ColumnShell`, a sidebar that runs to the window's top with the traffic lights, beside one or two panes that bring their own headers; tested
 - [ ] G8 Issue #6: a Layout story, `stories.json`, AGENTS.md and the PRD line; the story runs live on the site
 - [ ] G9 Push, deploy, reply on #6 and #7, close #6