feat(web): design tokens, Tailwind config, base components (TEC-3057)

- Add chart palette, motion, and z-index CSS vars to globals.css
- Replace custom theme-provider with next-themes (dark default)
- Extend tailwind.config.ts with heading fonts, spacing (row-compact,
  row-roomy, sidebar), chart colors, elevation shadows, glow shadows,
  transition timing, pill border-radius, z-index scale
- Update tick-flash animations to match design token spec (480ms)
- Add prefers-reduced-motion support for all animations
- Create base design-system components:
  Surface, SurfaceElevated, Divider, DensityProvider/useDensity,
  Numeric (VND/percent/compact formatting), Signal (up/down/neutral pill)
- Add dev-only /dev/tokens showcase route (404 in production)
- Update theme-provider tests to match next-themes integration

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/components/design-system/divider.tsx

@@ -0,0 +1,28 @@
+import { cn } from '@/lib/utils';
+
+export interface DividerProps extends React.HTMLAttributes<HTMLDivElement> {
+  /** Use border-strong variant for headers/section separators. */
+  strong?: boolean;
+  /** Orientation. Default horizontal. */
+  orientation?: 'horizontal' | 'vertical';
+}
+
+export function Divider({
+  strong = false,
+  orientation = 'horizontal',
+  className,
+  ...props
+}: DividerProps) {
+  return (
+    <div
+      role="separator"
+      aria-orientation={orientation}
+      className={cn(
+        strong ? 'bg-border-strong' : 'bg-border',
+        orientation === 'horizontal' ? 'h-px w-full' : 'h-full w-px',
+        className,
+      )}
+      {...props}
+    />
+  );
+}