Promote the live exposure preview to the primary workspace

[Today20092]

What to build

Make the live exposure preview the primary LUT-building workspace. It spans the page width at the top, keeps selected-band editing and LUT actions close to the graph, and moves general configuration, exposure-band management, and encoded-signal warnings underneath.

Acceptance criteria

• The live exposure preview appears before the configuration surfaces and uses the full available page width.
• Selected-band controls and Generate, Import, and Export actions remain close to the preview.
• Configuration, exposure-band management, and encoded-signal warnings appear below the preview in a responsive layout.
• The layout remains usable without horizontal overflow on narrow viewports.
• Existing preview, configuration, import/export, and generation behavior remains functional.

Blocked by

None — can start immediately.