feat: support user-entered text in code blocks in bold

[dwmkerr]

Summary

In the book manuscript, user-entered text is shown in bold within command examples. For example:

$ **ls -al**
output here

The $ prompt is regular weight, but ls -al (what the user types) is bold.

Current Behavior

Our bash-formatted code blocks don't support inline bold styling:

$ ls -al
output here

Everything renders in the same weight.

Desired Behavior

Find a way to visually distinguish:

• Prompt ($) - regular weight
• User input (ls -al) - bold or highlighted
• Output - regular weight

Options to Explore

1. Custom code block component with markup parsing
2. CSS-based solution using syntax highlighting classes
3. Different approach (e.g., separate prompt/input/output blocks)

Context

This is a migration issue - the book uses this convention throughout to help readers distinguish what they should type vs. what they'll see.