fix(link-dialog): hide the copy button when the Clipboard API is unavailable

[Misyuk-T]

fixes #990

• navigator.clipboard is undefined outside secure contexts, so the copy button in the link preview threw a TypeError over plain http (non-localhost origin)
• LinkDialog now renders the copy button only when navigator.clipboard.writeText exists. everything else in the preview (open, edit, remove) is untouched
• went with hiding over an execCommand('copy') fallback: it's deprecated and the issue itself suggests making the action optional
• added src/test/link-dialog.test.tsx: no button without the Clipboard API, writeText called with the url when it's there. the first test fails without the fix
• npm run lint, npm run typecheck, npm run test:once, npm run build all pass

[petyosi]

Thanks for this! I pushed a follow-up commit (ca2a284) on top of yours that falls back to document.execCommand('copy') instead of hiding the button. Hiding it removed copying for exactly the setup in #990, an intranet app served over plain http.

What changed:

• If navigator.clipboard.writeText is missing, the URL is copied from a temporary off-screen textarea. Focus and the previous selection are restored afterwards.
• If writeText rejects (for example, when a permissions policy blocks clipboard-write), the same fallback runs. This also gets rid of the unhandled rejection.
• "Copied!" appears only when the copy actually succeeded.
• The button is hidden only when neither path can copy.

I checked it in Chromium on a non-localhost http origin (isSecureContext === false): the URL reached the system clipboard. The tests cover the fallback, the rejection path and the failure case.

Let me know if anything looks off to you.

[github-actions]

🎉 This PR is included in version 4.3.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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