feat(ui): visual polish primitives + token additions (Phase A)

Adds the design tokens the polish PRs (10a-e) will draw from:
shadow-xs/sm/md/lg/glow, radius scale tuned to spec, gradient utilities,
spring/smooth eases, and fast/base/slow durations. Introduces
StatusPill, KPITile, and EmptyState primitives plus a polished
PageHeader variant ('gradient') with optional eyebrow + KPI sub-line —
existing PageHeader callers stay on the plain variant.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/ui/empty-state.tsx

@@ -0,0 +1,33 @@
+import * as React from 'react';
+
+import { cn } from '@/lib/utils';
+
+interface EmptyStateProps {
+  icon?: React.ReactNode;
+  title: string;
+  body?: React.ReactNode;
+  actions?: React.ReactNode;
+  className?: string;
+}
+
+export function EmptyState({ icon, title, body, actions, className }: EmptyStateProps) {
+  return (
+    <div
+      className={cn(
+        'flex flex-col items-center justify-center gap-3 rounded-lg border border-dashed border-slate-200 bg-white px-6 py-12 text-center',
+        className,
+      )}
+    >
+      {icon ? (
+        <div className="flex h-14 w-14 items-center justify-center rounded-full bg-gradient-brand-soft text-brand">
+          {icon}
+        </div>
+      ) : null}
+      <div className="text-base font-semibold text-foreground">{title}</div>
+      {body ? <div className="max-w-md text-sm text-muted-foreground">{body}</div> : null}
+      {actions ? (
+        <div className="mt-2 flex flex-wrap items-center justify-center gap-2">{actions}</div>
+      ) : null}
+    </div>
+  );
+}