fix(profile): improve copy invite link feedback and accessibility

[lucasvass1]

What

Improved the "Copy invite link" feedback on the profile page beyond a subtle text swap:

• Added a checkmark icon + emerald color on success (matching the success color pattern already used elsewhere in the app, e.g. login resend confirmation)
• Added a visually-hidden aria-live status region so screen readers announce the copy result
• Clipboard failures now show a visible error message instead of failing silently

How to test

1. Log in and go to /profile
2. Click "Copy invite link" — confirm checkmark + "Copied!" appears, link is actually on clipboard, resets after 2s
3. Tested in Chrome and Firefox
4. To test the failure path: in DevTools console, run navigator.clipboard.writeText = () => Promise.reject() then click the button — confirm the error message shows without crashing

Closes #18

[FrankezeCode]

Awesome