Improve exposure-graph feedback

[Today20092]

Parent

• Redesign the LUT Builder workflow and interface #23

What to build

Make the exposure graph communicate its scale, reference point, selected band, and monitored range at a glance while preserving its existing pointer and keyboard editing behavior.

Acceptance criteria

• The graph visibly identifies its current unit, including stops from the reference point when operating in stops mode.
• The zero/reference position is visually emphasized without overpowering band colors.
• A concise readout identifies the selected band, center value, and half-width or boundary information appropriate to the active mode.
• The selected band's center and range boundaries are distinguishable without relying solely on color.
• Selection remains synchronized in both directions between graph markers and band rows.
• Pointer dragging, wheel stepping, arrow-key movement, and width adjustment preserve their current semantics.
• Tick labels and supporting graph text remain readable at the supported viewport sizes.
• Off-scale band feedback remains available and understandable.
• Existing exposure-graph interaction tests are updated only for externally observable labels or behavior.
• Existing automated tests and the frontend production build pass.
• The graph is manually verified with one band, multiple overlapping bands, fill mode, and an off-scale selection.

Blocked by

• Establish the LUT-building workflow hierarchy #24