test(frontend): cover CopyToClipboard permission-denied feedback

[utksh1]

Summary

Add tests for clipboard rejection and verify the UI gives accessible failure feedback without throwing.

Scope

• Suggested file: frontend/src/components/CopyToClipboard.tsx
• Add or extend a focused frontend unit test.
• Do not bundle unrelated visual or production changes.

Acceptance criteria

• The behavior is covered with a deterministic test.
• The user-visible or accessibility outcome is asserted.
• Existing tests remain stable.
• The focused frontend test passes.

Verification

Run the affected Vitest file from frontend/.