feat(ui): consolidate and simplify how we use colors

* reconciles latest color variables from Figma
* defines the primary colors and the color system in tailwind config.
* refines how we generate utilities within the color system for `bg`, `fg` and `border`.
* removes custom box shadows, instead leaning on direct definition in CSS and `theme()`.

This change removes duplicate color information being defined as CSS variables in `index.css`
and co-locates all style information with the component
whilst retaining the ability to tie in to the color system when mapping styles from Figma.

pkgs/clan-app/ui/package.json

@@ -11,6 +11,7 @@
     "serve": "vite preview",
     "check": "tsc --noEmit --skipLibCheck && eslint ./src --fix",
     "test": "vitest run --project unit --typecheck",
+    "vite": "vite",
     "storybook": "storybook",
     "knip": "knip --fix",
     "storybook-build": "storybook build",