fix: show correct embed prompt for GitHub issue vs pull request

[liu971227-sys]

Summary

• add optional prompt label support to paste-format menu
• detect GitHub URL type and show contextual prompt text
• show Embed Pull Request? for /pull/ URLs and Embed Issue? for /issues/ URLs

Scope

• cloud editor
• shared editor hook
• mobile editor

Closes #1149

[liu971227-sys]

For payout submission via IssueHunt, I am currently blocked by persistent HTTP 401 on IssueHunt side (auth/session mapping problem), despite re-login, OAuth revoke/re-authorize, and cookie/storage reset.

• IssueHunt page: https://oss.issuehunt.io/r/BoostIO/BoostNote-App/issues/1149
• Timestamp: 2026-02-16 11:34:31 +08:00

I have opened a support request with IssueHunt and requested account-session reset. Please keep this PR bounty-eligible while that gets fixed.

[liu971227-sys]

Update: I pushed one follow-up commit to cover the realtime preview editor path as well.\n\n- Commit: e9ddd952\n- File: src/cloud/components/DocPreview/DocPreviewRealtime.tsx\n- Change: show the same GitHub issue/PR prompt label in the shortcode conversion menu (and keep menu border radius behavior correct after adding the label row).\n\nThis keeps behavior consistent with the editor/mobile paths already fixed in this PR.