feat(viewer): align design-token values to the mockup palette (#1365)

Update the light :root and dark palette values to the authoritative mockup
palette and add the interactive tokens (input/tag/row/marked/pagination/
scroll/code-diff) the per-screen work needs. Keeps the existing variable
names and ocr's prefers-color-scheme model (no data-theme, no JS toggle).

The mockup accent green (#17cb4b) is used for fills/borders/active states;
--link and green text keep a darker green (#177d35) that clears WCAG AA on
light surfaces, and revert to the bright accent on dark surfaces where it
already has enough contrast.

Closes #1361.