feat: hierarchy UI — org chart tree visualization

[aterrylu]

Summary

• Org chart panel — top-down tree visualization using react-organizational-chart with glassmorphism cards, gradient accent borders (blue→purple for working, green→teal for idle), and glow effects on active agents
• Sidebar integration — ORG CHART section in sidebar matching AGENTS/PROJECTS style, with "View hierarchy" toggle
• Error handling — distinguishes "no agents" from "server error" / "cannot reach server" with auto-retry indicator

Visual design

State	Card style
Working	Blue→purple gradient top accent, blur glow, italic status
Running (idle)	Green→teal gradient top accent, subtle glow
Stopped	Dim borders, muted text

Files

File	Changes
HierarchyPanel.tsx (new)	Tree panel with react-organizational-chart, agent cards, status resolution, error states
Sidebar.tsx	ORG CHART section with view toggle
SessionViewManager.tsx	"hierarchy" view mode rendering
Header.tsx	Removed header button (moved to sidebar)
Codicon.tsx	Added type-hierarchy icon
store.ts	setViewMode action, "hierarchy" in view mode union, persistence guard (hierarchy is transient)
dashboard/package.json	Added react-organizational-chart dependency

Test plan

• Biome lint clean (44 files)
• Dev server tested locally — tree renders with live agent status
• Hierarchy view mode toggle works from sidebar
• Close button returns to terminal view
• Error state shows when server is unreachable
• Hierarchy view not persisted across page reloads (transient)
• Dependency in correct package.json (dashboard, not root)

🤖 Generated with Claude Code

[nox-0x]

🟢 Suggestion

Problem: When a polling refresh fails (server error or network hiccup), setError(...) fires but setChart is not reset. Since HierarchyContent renders the error state before checking chart.length, the previously-loaded tree disappears entirely during transient failures.

Why it matters: With a 5-second poll interval, a single blip causes the user to lose their tree view momentarily and see an error. For a monitoring panel this is jarring — stale data is almost always preferable to a blank error screen.

Suggested fix:

// Show stale data + a non-blocking error banner instead of hiding the chart.
// In HierarchyContent, swap the error check order:
if (chart.length > 0 && error) {
  // render tree AND a dismissible warning banner at the top
}
if (error && chart.length === 0) {
  // only show full error state when there is nothing to show
}

Or simpler: keep chart populated on error, and render a small toast/banner overlay rather than replacing the full panel.

[nox-0x]

Clean, well-structured hierarchy panel. Cancellation logic in the polling hook is correct, the transient view-mode guard in the store is a nice touch, and the error/empty states are thoughtfully separated. Left one non-blocking suggestion: stale chart data should be shown alongside a transient error rather than replaced by it, which would make the panel more resilient to brief network hiccups. Good to merge.