Add the structural navigation layer.

Frames as slides:

• Frames already exist as back-band containers with titles. Add "presentation mode": sort frames top-to-bottom then left-to-right (reading order), animate the viewport to fit each frame's bounds with padding (viewportForRect helper), navigate with next/prev buttons and arrow keys, Escape exits. Hide docks/panels while presenting.
• Dragging a frame moves the elements contained within its bounds along with it.

Minimap (bottom-right):

• A second small rendering the whole board's bounds scaled to fit, with a viewport rectangle showing the current view. Click or drag on the minimap to navigate (inverse mapping minimapToWorld). Keyboard accessible: focusable, arrow keys pan. Re-render it from the same coalesced render effect.

Board search:

• Ctrl/Cmd+F opens an in-board search input (suppress the browser's). Match against note and text content case-insensitively; show "n of m"; Enter/arrows step through matches wrapping around; each step glides the viewport to the match and selects it. Escape closes.

Acceptance: presentation mode walks frames in reading order full-screen; the minimap navigates and stays in sync; search finds, steps, glides and wraps.