fix(docs): resolve color token values so swatches render in docs pages

[maarkN]

Fixes #760

Problem

On the docs Design System pages (yarn docs:dev → Background Color, Border Color,
Text Design › Text Color), all color swatches render transparent/empty — the colors
don't show up.

Root cause

The semantic color tokens generated in tailwind/colorPalette.js resolve to Tailwind
strings containing the internal <alpha-value> placeholder, e.g.:

color-mix(in srgb, var(--surface-gray-2, #F3F3F3) calc(<alpha-value> * 100%), transparent)

That placeholder is only substituted by Tailwind when generating utility classes.
docs/content/docs/design-system/[token].paths.ts was passing this raw value to the
token components, which use it as an inline style (backgroundColor / color /
borderColor) — invalid CSS, so the swatches rendered transparent.

Fix

Added a small resolver in [token].paths.ts that extracts the theme-aware
var(--token, fallback) portion of the value and applied it in the three color
getters (getBgColors, getTextColors, getBorderColors). Since the CSS variables
are defined on :root / [data-theme="dark"] by the theme plugin, the swatches also
follow dark mode correctly.

Before / After

Dark mode (swatches follow the theme):

Also fixes Border Color and Text Design › Text Color, which used the same data: