0.2.0-preview.1 — PNG and sized renditions

Adds signed PNG/WebP rendition selection by explicit target pixel dimensions. The SDK validates the rendition contract, content hashes, decoded type and exact pixel size; malformed or unavailable candidates fall back to the next verified candidate, legacy WebP, cached history, then the bundled image.

Existing schema-1 manifests and caches remain supported. SVG sources are prepared by Assetlib into native raster fallbacks; this release does not add native SVG rendering. SwiftUI still receives ordinary Image values through the observable image store.

Validation: 17 executed Swift tests, 65 shared signed contract cases, four shared size selections, PNG decoding and offline restart, code generation, and release build. Generic iOS and Simulator demo compilation passed; manual iPhone UI acceptance is separate.