Builds an annotated code-walkthrough page, the source pinned on the left, explanations scrolling on the right, with the lines under discussion spotlit as you scroll. Use when the user asks to "walk through" a file or diff, wants code "explained line by line", or asks for a "code walkthrough", "annotated source", "explain this migration", or a page explaining what code does and why. Themed Catppuccin Mocha.
