improvement(plugins-page): Refactor using card

I've (hackily so) written my own plugin card to replace the previous
usage of the `Checkbox` component.
Beware, ye who tread these lands, for they are decrepid.

src/components/ui/Checkbox.tsx

@@ -3,7 +3,7 @@ import styled, { css } from "styled-components/macro";
 
 import { Children } from "../../types/Preact";
 
-const CheckboxBase = styled.label`
+export const CheckboxBase = styled.label`
     gap: 4px;
     z-index: 1;
     display: flex;
@@ -52,7 +52,7 @@ const CheckboxDescription = styled.span`
     color: var(--secondary-foreground);
 `;
 
-const Checkmark = styled.div<{ checked: boolean; contrast?: boolean }>`
+export const Checkmark = styled.div<{ checked: boolean; contrast?: boolean }>`
     margin: 4px;
     width: 24px;
     height: 24px;