The Board shell: agent supervisor card view.

Displays agent sessions as cards on a spatial grid. Each card shows task description, status, model, and elapsed time. Clicking a card (or pressing Enter) zooms into its workspace for full editing.

The Board stays the active shell even when zoomed into a card. In grid mode, it renders the card grid and handles navigation input. In zoomed mode, it delegates rendering and input to the traditional editor pipeline for the active card's workspace.

Two rendering modes

• Grid view (zoomed_into: nil): card rectangles with status badges, task text, and model labels. Board-specific input handlers.
• Zoomed view (zoomed_into: card_id): full editor rendering using the card's restored workspace. Traditional input handlers plus an Escape binding to zoom back out.