fix(AddressDisplay): add copy fallback and tests for truncation, clipboard, and timer reset (#604)

[stayzappy]

Closes #604

Summary

• Added document.execCommand("copy") fallback when navigator.clipboard.writeText rejects or is unavailable.
• Updated aria-label to "Copied!" upon copy success.
• Added unit tests in AddressDisplay.test.tsx:
  • Truncated address rendering by default.
  • Full untruncated address copied on button click.
  • Fake timer reset after 2000ms back to "Copy address".
  • Fallback triggering execCommand on clipboard.writeText failure.
  • Error resilience when both clipboard API and fallback throw.