fix: mention insertion on iOS

[IvanIhnatsiuk]

Summary

This pull request refines how mentions are inserted into the text editor, focusing on improving the user experience and ensuring the correct handling of text selection and formatting. The main changes involve batching text insertions, updating selection logic, and ensuring that formatting is preserved.

Mention insertion and selection handling improvements:

• Batches the insertion of the mention and the trailing space using beginEditing/endEditing to ensure atomic updates and prevent intermediate state issues.
• Updates the selection only after both the mention and the separator are inserted, ensuring the separator remains plain text and outside the mention formatting.
• Ensures the text view is focused after insertion, if necessary, to maintain a smooth editing experience.
• Updates the recently changed range to cover both the mention and the trailing space, improving downstream handling of text changes.

Test Plan

1. Open the editor screen
2. Press on the "@" in toolbar
3. Select any user
4. Observe that metnion was successfully inserted

Screenshots / Videos

Screen.Recording.2026-07-30.at.18.58.58.mov

Compatibility

OS	Implemented
iOS	✅❌
Android	✅❌

[Copilot]

Pull request overview

Refines iOS mention insertion in the rich text editor to avoid intermediate editing states and ensure selection/formatting behave correctly when inserting a mention plus a trailing separator.

Changes:

• Batch mention + trailing space insertion using textStorage beginEditing / endEditing for a single atomic text storage update.
• Move selection update to after both insertions, keeping the separator outside mention formatting.
• Ensure the text view is focused before applying the final selection, and expand recentlyChangedRange to include both the mention and trailing space.

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