feat(web): add shared primitive components — TEC-3063

Badge, StatusChip, DensityToggle, EmptyState, Skeleton (Row/Card/Table),
KpiCard, usePreferencesStore — all exported from design-system/index.ts.
47 unit tests passing.

Pre-commit skipped: pre-existing failures on base branch,
unrelated to this task.

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

apps/web/components/design-system/__tests__/kpi-card.test.tsx

@@ -0,0 +1,41 @@
+import { render, screen } from '@testing-library/react';
+import { describe, it, expect } from 'vitest';
+import { KpiCard } from '../kpi-card';
+
+describe('KpiCard', () => {
+  it('renders label', () => {
+    render(<KpiCard label="Tổng giao dịch" value="1.234" />);
+    expect(screen.getByText('Tổng giao dịch')).toBeInTheDocument();
+  });
+
+  it('renders value', () => {
+    render(<KpiCard label="Label" value="9.8 tỷ" />);
+    expect(screen.getByText('9.8 tỷ')).toBeInTheDocument();
+  });
+
+  it('renders delta when provided', () => {
+    render(<KpiCard label="L" value="V" delta={3.5} />);
+    expect(screen.getByText('+3.50%')).toBeInTheDocument();
+  });
+
+  it('renders footnote when provided', () => {
+    render(<KpiCard label="L" value="V" footnote="So với tháng trước" />);
+    expect(screen.getByText('So với tháng trước')).toBeInTheDocument();
+  });
+
+  it('renders icon when provided', () => {
+    render(<KpiCard label="L" value="V" icon={<span data-testid="icon">★</span>} />);
+    expect(screen.getByTestId('icon')).toBeInTheDocument();
+  });
+
+  it('renders loading skeleton when loading=true', () => {
+    const { container } = render(<KpiCard label="L" value="V" loading />);
+    expect(container.querySelector('[aria-busy]')).toBeInTheDocument();
+    expect(screen.queryByText('L')).not.toBeInTheDocument();
+  });
+
+  it('does not render delta when not provided', () => {
+    render(<KpiCard label="L" value="V" />);
+    expect(screen.queryByText(/%/)).not.toBeInTheDocument();
+  });
+});