IDE-style HTML view of a change, an issue, or both

Renders a single, self-contained HTML file: a file tree on the left, a diff/code/doc editor top-right, and an explanation pane bottom-right. No server, no CDN, opens correctly via `file://`. The goal is aiding human understanding of what's happening in a change — a walkthrough or presentation of it, not a raw diff dump — whatever that change actually is: a **worktree** (uncommitted local work), a **branch** (against the default branch), or an **issue** (before any code exists at all). Standalone — nothing here depends on any other plugin, and it stays that way deliberately, since it needs to work on projects that can't or don't adopt spec-flow. Two modes — pick determinis…