fix(ui): remove self-referential --shadow-*/--tracking-normal declarations in @theme inline

[rawdaymx]

Fixes #1241

What changed

@theme inline declared nine custom properties (--tracking-normal, --shadow-2xl through
--shadow-2xs) as var() references to themselves. Per the CSS custom-properties spec, a
property that references itself is invalid at computed-value time and falls back to the
property's initial value (none for box-shadow, normal for letter-spacing) — so every
shadow-*/tracking-* utility, including button.tsx's own shadow-xs, rendered with no
visible effect.

This PR is a pure deletion of the nine circular lines. With them gone, Tailwind CSS 4.3.2's own
built-in defaults (tailwindcss/theme.css) apply automatically.

Verification

Compiled default.css with Tailwind CSS 4.3.2 (@tailwindcss/postcss) against a template using
shadow-xs and tracking-wide, before and after:

	before	after
.shadow-xs compiled box-shadow	unresolvable var(--shadow-xs), computed none	0 1px 2px 0 rgb(0 0 0 / 0.05) (real shadow)
--tracking-normal	var(--tracking-normal) (circular)	0em
.tracking-wide computed letter-spacing	normal	calc(0em + 0.025em)

pnpm --filter @chatbotx.io/ui check-types and pnpm --filter @chatbotx.io/ui test both pass
(13/13 test files, 56/56 tests) against this change.

Note

If the intent was custom (non-default) shadow/tracking values rather than Tailwind's stock
defaults, the maintainer may prefer literal values instead of a plain deletion — happy to adjust.