feat: add glassmorphism design system

Dark-first color palette, glass surface styles with blur
backing, typography with text shadows, and spacing constants.

src/theme/index.ts

@@ -0,0 +1,5 @@
+export { colors } from "./colors";
+export { glassSurface, glassIntensity, glassRadius, glassBorder } from "./glass";
+export type { GlassVariant } from "./glass";
+export { typography } from "./typography";
+export { spacing, layout } from "./spacing";