Remove supra brand from design system

Supra (VivoKey MD3 theme) has been extracted into a standalone
Dangerous-Pi theme plugin. Remove all supra references from tokens,
web CSS, showcase apps, and documentation.

- Delete supra brand tokens and elevation.css
- Update ThemeBrand type to "dt" | "classic"
- Remove supra from CSS generation, imports, and bevels
- Update CLAUDE.md and package READMEs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/tokens/src/index.ts

@@ -10,15 +10,13 @@ export type {
 
 export { dt } from "./brands/dt.js";
 export { classic } from "./brands/classic.js";
-export { supra } from "./brands/supra.js";
 
 import { dt } from "./brands/dt.js";
 import { classic } from "./brands/classic.js";
-import { supra } from "./brands/supra.js";
 import type { BrandTokens, ThemeDefinition } from "./types.js";
 
 /** All brand tokens keyed by id */
-export const brands: Record<string, BrandTokens> = { dt, classic, supra };
+export const brands: Record<string, BrandTokens> = { dt, classic };
 
 /** Theme registry for UI selectors */
 export const themes: ThemeDefinition[] = [
@@ -36,11 +34,4 @@ export const themes: ThemeDefinition[] = [
     supportsModes: ["dark", "light", "auto"],
     defaultMode: "dark",
   },
-  {
-    id: "supra",
-    name: supra.name,
-    description: supra.description,
-    supportsModes: ["dark", "light", "auto"],
-    defaultMode: "dark",
-  },
 ];