The plan now lives IN the chat (plan blocks, wave-4 item 3) and background
processes live in the activity dock (item 1), so the right sidebar's
tree panel + sub-agent fleet column is retired from the chat view:
- delete components/tree-panel.tsx (three-mode rail/list/graph panel) and
components/sub-agents-panel.tsx; their graph interaction machinery lives
on in plan-block.tsx and fleet observability in activity-dock.tsx.
- app/layout.tsx drops TreePanelModeProvider (the mode no longer exists).
- chat.tsx drops the xl:flex right column; the middle column is the view.
- tests: render-tree-panel.test.tsx deleted; the sub-agents panel suite
removed from demos.test.tsx (dispatch cards' jobs-context stays — the
central poll drives transcript dispatch cards).