refactor!: drop the token mirror, leaving the stylesheet as the only copy

[YaelAnaya]

Stacked on #7. Review that one first; this PR's diff is only the removal.

src/theme/tokens.ts held LIGHT_THEME, DARK_THEME, THEME and cssVar: a TypeScript copy of the values in styles.css, kept for a caller that could not read CSS, plus a test to hold the two in step.

Nothing in the package imported it. No consumer imported it either. A second copy of the palette is a second thing that can go stale, and ninety-seven hand-maintained lines plus a synchronisation test to protect a caller that never arrived.

What replaces it

A caller that genuinely needs a value as a string reads it from the document, which has the further advantage of answering for the theme the reader is in:

const ink = getComputedStyle(document.documentElement).getPropertyValue("--foreground");

Everywhere else, var(--role).

The test keeps the half that was never about the mirror

Every role declared in both themes and nothing else, the palette closed, one --color-<role> per role, the radius scale derived from --radius, dark mode keyed off the class, no focus geometry in the base layer.

The dark-theme check that compared against the mirror now asserts something the mirror could not: that the theme repoints its roles rather than restating the light values.

	Before	After
Token contract tests	15	13
Hand-maintained duplicate lines	97	0

Adding a token now touches one place fewer.

Breaking change

LIGHT_THEME, DARK_THEME, THEME and cssVar are no longer exported. docs/MIGRATION-0.3.md gains section 6 with the replacement; the "Unchanged" entry that promised they were kept is corrected.

Verification

pnpm verify passes: format, lint, 124 tests in 16 files, the build, the docs site, and the packed-consumer test.