[upstream #16481] Field fill and ink need theme roles

[berry-13]

The shared field (Input, fieldControl in packages/client/src/components/Field.ts) paints bg-transparent and inherits text-text-primary, so no theme can give a field its own fill or ink.

Click UI: click.field.color.background.default is #fbfcff light and rgb(17.794% 17.794% 17.794%) (about #2d2d2d) dark, and click.field.color.text.default is #302e32 light and #e6e7e9 dark (tag v0.12.0, e2b3d21).

LibreChat under the ClickHouse theme: the field is transparent over its host surface (dark: #1f1f1c, deltaE2000 5.1 from Click UI's fill) and its ink is the body text-primary (#161517 / #ffffff, deltaE2000 8.1 / 5.1). The parity spec pins both as not expressible in light and dark.

Why no existing role closes it: the default field is transparent, and a colour role is an opaque triplet, so a fill role needs a default that reproduces "no fill" (an alpha companion such as --field-fill-alpha: 0, the way border-light carries one). The ink needs a role whose default is text-primary in every bundled theme.

Expected: a field fill role (default transparent) and a field ink role (default text-primary) that fieldControl reads, the ClickHouse theme setting both from Click UI, and the two not-expressible entries in clickui.spec.ts removed.

[berry-13]

Closed by reviewctl followups sync: LibreChat-AI#16544 merged on 2026-09-30 at a1b98bc.

[berry-13]

Reopened: the follow-up sync closed this because LibreChat-AI#16544 mentioned it, but that PR only lists this gap as still not expressible; it is not fixed. The PR body now links it without the closing reference.