ADR-0141 Selection is a shape, not a hue

Amends: ADR-0139

#Context

ADR-0139 moved a selected Button off the flat surface's blue and onto the tier's accent pair, accent-subtle and text-accent, so a selected key in field-night was the night hue. In field-day the pair is still blue, and on the helm display the selected Alarms key was the one blue thing on a screen whose hue otherwise means a reading: green in range, amber in caution, red in alarm. Reviewed on the display, the blue key was read as out of place.

#Decision

A selected Button is the page ground, the primary ink, and a heavy outline in that ink. selected-color resolves to surface-page and on-selected-color to text-primary; the stylesheet draws the outline at border-heavy and sets the label bold. Selection is a shape in every theme: a dark ring in field-day, a thin line in the night hue in field-night.

#Rejected options

Keep the accent pair. It is what ADR-0139 decided, and a selected key is easy to find in it. It lost because a selected key is a state of a control, not a reading, and on an instrument screen hue is spent on readings.

Invert the key: primary ground, page ink. The strongest mark available. It lost in field-night, where a filled key in the primary ink is the brightest block on the screen and spends the dark adaptation the theme exists to keep.

#Consequences

No scene moved. No fixture renders a selected button; the docs contrast check passes unchanged.