Visualize how behavior evolves across versions.

Renders the version lineage as a tree - the main line as a vertical trunk, with
branches created by 'dow commit --from' off to the side - annotating each step with
its drift and stability change. Use --mermaid for a Mermaid gitGraph, or -o FILE to
write it to a Markdown file you can preview.

@examples
dow tree
dow tree -o evolution.md
