Emoji autocompletion will overwrite an immediately preceding emoji

[wjaaaaaaat]

Issue Description

When using emoji autocompletion immediately following another emoji, pressing tab to create the new emoji will delete the immediately preceding emoji.

Screen recording:
https://github.com/user-attachments/assets/db415030-ac5a-42d7-9400-f4f8dcb52cf3
(ignore the head shaking emoji rendering wrong in the suggestions, that's an issue on my end)

Expected Behavior

The new emoji should be created without deleting the preceding emoji.

Actual Behavior

The preceding emoji is deleted when the new emoji is created.

Reproduction Steps

1. Open Cinny, log in, and navigate to a room.
2. Type an emoji using tab completion (ex. type ":skull" then press tab).
3. Move the text cursor to the immediate right of the emoji (or delete the trailing space if there is one).
4. Type another emoji using tab competion (ex. type ":poop" then press tab).

Environment

- OS: Arch Linux
- Browser: Firefox 152.0.4
- Cinny Web Version: v4.12.6 (app.cinny.in)
- Matrix Homeserver: matrix.org

Relevant Logs

No response

Additional context

No response

I acknowledge that:

• I have searched the Cinny repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.