0.2.1-preview.1 — Localized artwork descriptions

Adds optional localized descriptions paired with the actual delivered image and its signed release. Description lookup uses an exact language tag, progressively less specific tags, then the explicit default. Cached historical artwork keeps its own description.

SwiftUI still receives native Image values. The new AssetArtwork snapshot and generated coastArtwork(locale:requireDescription:) helper let an informative usage keep bundled artwork when remote metadata is missing. Apps explicitly choose descriptive labels, decorative hiding, and control labels.

Validation: Swift tests and code generation, 82 shared signed contract cases, release build, generic iOS and Simulator compilation, and a macOS native accessibility-tree probe covering English/Thai descriptions, cached/offline artwork, disconnect, decorative hiding, and an action button. Exact source CI passed: https://github.com/AssetLib/sdk-swift/actions/runs/37729542543

This is a developer prerelease. Full VoiceOver listening and iPhone runtime acceptance remain unverified.