Disable rich editor toolbar for plaintext editor

- Rich editor toolbar must be shown only for rich editor
- For case with split editor, we can make a buttons disabled always except a moment user focus rich editor, or force focus on rich editor when user click any button

Current state:

<img width="1382" height="1007" alt="Image" src="https://github.com/user-attachments/assets/58314730-a80b-4198-936c-baba197880d5" />