Add interactive DisplayList preview

AGENTS.md

@@ -16,3 +16,4 @@
 
 - Keep the preview server running after verification so the user can open it. Report the complete HTTP URL, including the `/DisplayListExplorer/` base path.
 - If the default preview port is occupied, reuse the existing server when it serves this worktree; otherwise choose another port and report it explicitly.
+- Open the exact local URL printed by Vite (normally `http://127.0.0.1:4173/DisplayListExplorer/`) rather than a `file://` URL.

README.md

@@ -11,6 +11,8 @@ The parser and converter are written in Swift. [JavaScriptKit](https://github.co
 - Reproduces the single-line formatting emitted by `SExpPrinter`.
 - Links source and `minimalDescription` ranges with bidirectional hover highlighting.
 - Provides dedicated `minimalDesc`, encoding info, and occurrence statistics tabs.
+- Previews DisplayList frames inside draggable iPhone presets or a custom-size Window frame, with
+  zoom, fit, actual-size controls, a point ruler, resolved content, effects, and payload placeholders.
 - Highlights every matching source range when a statistics row is hovered or focused.
 - Copies compact, self-contained links that reopen a shared `minimalDescription`.
 - Runs entirely in the browser; pasted descriptions are not uploaded.