Add interactive DisplayList preview

[Kyle-Ye]

Summary

• parse full DisplayList descriptions into a renderable preview model, including colors, text, paths, effects, and approximation fallbacks
• render previews in Canvas with iPhone device frames or a custom Window size
• add fit, editable zoom, a scale ruler, drag-to-pan, trackpad pinch, and touch pinch gestures
• refresh the preview controls, device picker, default iPhone 17 Pro sample, and tab icons
• document the required local SwiftWasm preview workflow

Why

The explorer previously showed only the encoded minimal description and metadata, which made it difficult to understand the visual result of a captured DisplayList. The first interaction pass also handled only a single pointer, so browser trackpad and two-touch pinch gestures could not update the preview scale.

User impact

Users can now inspect an approximate visual rendering inside realistic device or window frames, move and scale the canvas directly, enter an exact zoom percentage, and understand which nodes required approximation.

Validation

• swift test — 15 tests passed
• SwiftWasm release build with the repository's Swift 6.2.3 toolchain
• production Vite preview build
• local preview endpoint returned HTTP 200

[github-actions]

Cloudflare Pages preview

Latest PR preview: https://pr-5.display-list-explorer.pages.dev

Commit	Immutable snapshot
722c729	Open snapshot

The PR URL always points to the latest deployment. Each commit snapshot is immutable.