fix(dropdown,box): drop menu-item prop leak; restore Box filter coverage

Two follow-ups from the PR 1150 review:

- Dropdown: DropdownMenuItemStyled spread `{...item}`, forwarding the Item
  fields (name/selected/label) onto the <li> as invalid DOM attributes.
  The spread was redundant — onClick already flows through getItemProps and
  label is rendered as children — so it is removed. Verified no consumer
  repo or test selects menu items by those attributes. (@ts-nocheck left in
  place; making the class compile-visible is tracked separately.)

- Box: restore Box.test.tsx as behavioural coverage for the shouldForwardProp
  filter — the one place the migration diverges from the mechanical rename.
  Asserts the migration contract (styled-system props stay out of the HTML),
  that genuine a11y attributes + click handlers still reach the element, and
  that polymorphic `as` works. Drives the click with userEvent.

tsc clean, 477/477 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JeanMarcMilletScality

src/lib/components/box/Box.test.tsx

@@ -0,0 +1,54 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { Box } from './Box';
+
+describe('Box', () => {
+  it('keeps design-system style props out of the rendered HTML', () => {
+    // Under styled-components v6 (which forwards unknown props to the DOM),
+    // Box must filter its open-ended styled-system props so they never surface
+    // as invalid HTML attributes on the element.
+    render(
+      <Box
+        mt={2}
+        bg="backgroundLevel1"
+        flexDirection="column"
+        alignItems="center"
+        justifyContent="space-between"
+        data-testid="b"
+      />,
+    );
+    const el = screen.getByTestId('b');
+    expect(el.hasAttribute('mt')).toBe(false);
+    expect(el.hasAttribute('bg')).toBe(false);
+    expect(el.hasAttribute('flexDirection')).toBe(false);
+    expect(el.hasAttribute('flexdirection')).toBe(false);
+    expect(el.hasAttribute('alignItems')).toBe(false);
+    expect(el.hasAttribute('justifyContent')).toBe(false);
+  });
+
+  it('forwards accessibility attributes and click handlers to the element', async () => {
+    const onClick = jest.fn();
+    render(
+      <Box
+        id="my-box"
+        role="region"
+        aria-label="a box"
+        data-custom="keep"
+        onClick={onClick}
+        data-testid="b"
+      />,
+    );
+    const el = screen.getByTestId('b');
+    expect(el.getAttribute('id')).toBe('my-box');
+    expect(el.getAttribute('role')).toBe('region');
+    expect(el.getAttribute('aria-label')).toBe('a box');
+    expect(el.getAttribute('data-custom')).toBe('keep');
+    await userEvent.click(el);
+    expect(onClick).toHaveBeenCalledTimes(1);
+  });
+
+  it('renders as the element given by the "as" prop', () => {
+    render(<Box as="section" data-testid="b" />);
+    expect(screen.getByTestId('b').tagName).toBe('SECTION');
+  });
+});

src/lib/components/dropdown/Dropdown.component.tsx

@@ -163,7 +163,6 @@ function Dropdown({
             <DropdownMenuItemStyled
               className="menu-item-label"
               key={item.label}
-              {...item}
               {...getItemProps({
                 item,
                 index,