[Bug]: docs: sp-grid toggle card usage in docs site is not working

### Code of conduct

- [x] I agree to follow this project's code of conduct.

### Impacted component(s)

Grid

### Expected behavior

- Space bar should toggle the card's checkbox state
- Page should not scroll when space bar is pressed on focused cards
- Cards should maintain their toggle functionality as they do in other contexts (e.g., Storybook examples)

### Actual behavior

- Space bar causes page scrolling
- Card checkbox does not toggle
- User cannot interact with cards using keyboard

### Screenshots

_No response_

### What browsers are you seeing the problem in?

Firefox, Chrome, Safari

### How can we reproduce this issue?

1. Navigate to the Grid component documentation or Storybook
2. Create a grid with cards that have `toggles="true"`
3. Tab to focus on a card in the grid
4. Press the space bar
5. **Expected**: Card checkbox toggles between checked/unchecked
6. **Actual**: Page scrolls down instead of toggling the card

### Sample code or abstract reproduction which illustrates the problem

```html

const grid = document.querySelector('#grid-demo');
grid.focusableSelector = 'sp-card';

grid.renderItem = (item, index, selected) => {
const card = document.createElement('sp-card');
card.toggles = true; // Cards should be toggleable
card.variant = 'quiet';
card.heading = `Card Heading ${index}`;
// ... other card setup
return card;
};

```

### Severity

SEV 4

### Logs taken while reproducing problem

_No response_

### Would you like to track this issue in Jira?

- [ ] Yes, please tell me the ticket number!

Start by reproducing the issue from the Grid component documentation or Storybook using the supplied sp-grid and sp-card example, then trace the Grid card focus behavior. Compare the docs-site behavior with the referenced Storybook examples; done means focused toggle cards respond to Space without scrolling in Firefox, Chrome, and Safari.

Written by the indexing model from the issue text.