fix(super-editor): insert mentions on first click

[malizhev]

Summary

• Prevent mention user rows from transferring focus or triggering the document-level selection handler on mousedown.
• Keep the existing mention popover mounted until its click handler inserts the selected user.
• Correct the internal inserMention prop typo to insertMention in the mention component and its caller.
• Add regression coverage for inserting a mention on the first click.

Why

Clicking a user in the mention popover currently requires two clicks. The first mousedown reaches the document-level custom-selection handler, which reapplies the editor state. Because the popover is still marked for an update, this remounts Mentions.vue before the browser can dispatch click to the original row.

Closes #3878

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[caio-pizzol]

Hey @malizhev, thanks for the fix! We reproduced the issue and confirmed that the implementation fixes first-click mention insertion.

I pushed a small follow-up to your branch so the regression test mounts into document.body. This ensures the test actually verifies that mousedown does not reach the document listener. Without it, the test stayed green even if .stop was removed.

The focused mention and popover tests are passing. Thanks again!