When switching from a code block with syntax highlighting to plain text, some residual highlighting remains and isn't fully removed.

When remove code block format, text keeps highlighted color without ability to clear. Reproduction Steps: Use the code block feature and enter content to generate as much syntax highlighting as possible, then switch to plain text. You'll notice that some highlighted keywords remain on the page. Expected Behavior: Switching to plain text should remove all syntax highlighting completely. <img width="977" height="331" alt="Image" src="https://github.com/user-attachments/assets/e31d9b87-53f3-4500-aea4-525567d556bc" /> version：2.0.3