add link to graphql playground on slices overview page

frontend/src/features/slices/overview/templates/SliceOverview.tsx

···
           </Button>
         </Card>
 
+        <Card padding="md">
+          <Text as="h2" size="xl" className="font-semibold mb-4 block">
+            🔍 GraphQL Playground
+          </Text>
+          <Text as="p" variant="secondary" className="mb-4">
+            Interactive GraphQL playground to query your slice's data.
+          </Text>
+          <Button
+            href={`https://api.slices.network/graphql?slice=${slice.uri}`}
+            variant="primary"
+          >
+            Open Playground
+          </Button>
+        </Card>
+
         {hasSliceAccess && (
           <Card padding="md">
             <Text as="h2" size="xl" className="font-semibold mb-4 block">