Create a better Explain UX

[d13]

The only way to explain commits today is through the "Explain Changes" button in the commit details panel, which limits its exposure to users. It also renders the output in a small window can be difficult to read depending on screen/panel size.

There are two primary goals for this task:

1. Expose the commit explanation feature in more places
2. Add more explain options
3. Open commit explanations in a markdown file where they can be easily read.

Expose the commit explanation feature in more places

• remove the existing "Explain Changes" button (and view) from commit details
• add an "Explain" button to the bottom of the commit message element
• allow users to explain a single commit from the graph via context menu
• allow users to explain multi-selected commits from the graph via context menu
• allow users to explain commits via a command in the command palette (similar to changelog generation flow)
• allow users to explain commits from the commits view
• allow users to explain commits from Search & Compare

Add more explain options

• explain a branch (from branch cards, from graph ref, from branches view, etc.)
• explain a wip

Open explanations in a markdown file

• remove the Explain (AI) section from the commit details
• open explanations in a markdown file
  • explore automatically opening the file in the markdown preview for easier reading
  • modify the output with new headers/sections (see image)
  • consider adding a linked sha for a single commit that opens the commit in the graph / commit details