Monospace the text inside of a code block when in edit mode

### What
When in note-editing mode (not preview, which already works) set the text inside of a code block (three ticks) similar to how inline code (one tick) does—monospaced and slightly lighter color.

### Why
For consistency and for ease of reading and writing code in blocks.

Start by locating the macOS note-editing mode and compare its inline-code styling with the code-block styling described in the issue. Done means text between triple backticks is monospaced and slightly lighter in edit mode, while preview behavior remains unchanged.

Written by the indexing model from the issue text.