[GUI] copyDelivery doesn't handle clipboard API failures

[Vantalens]

File: packages/gui/src/App.tsx:226

Severity: Low

Description:
navigator.clipboard.writeText() requires secure context and user permission; failure (HTTP, permission denied, or unsupported browser) throws unhandled promise rejection.

Code:

async function copyDelivery() {
  await navigator.clipboard.writeText(delivery || '');
}

Failure Scenario:

• User clicks 'Copy Delivery' button
• Browser blocks clipboard access (permission denied or HTTP context)
• Unhandled promise rejection logs to console
• No user feedback that copy failed

Suggested Fix:
Wrap in try/catch, show toast/notification on success/failure, fallback to textarea selection method.