perf(market): serve cached image variants

[bobleer]

Summary

• add lazily generated and disk-cached compact-v1 (640 px) and large-v1 (1280 px) image variants for MiniApp screenshots and Skin previews
• use responsive optimized images in both standalone market websites and BitFun embedded markets, with async decoding, lazy loading, and one-time original-image fallback
• preserve original image URLs and add immutable cache headers, ETags, bounded generation concurrency, and variant cleanup

Verification

• cargo test -p bitfun-miniapp-market-service -p bitfun-skin-market-service
• cargo check -p bitfun-miniapp-market-server -p bitfun-skin-market-server
• pnpm run check:core-boundaries:test && pnpm run check:core-boundaries
• pnpm run type-check:miniapp-market && pnpm run type-check:skin-market && pnpm run type-check:web
• pnpm run test:miniapp-market && pnpm run test:skin-market
• pnpm --dir src/web-ui run test:run src/infrastructure/api/service-api/MarketImage.test.ts
• pnpm run build:miniapp-market && pnpm run build:skin-market

Production validation

Deployed exact commit 1253ab70c4390fca0d1fc1141bc778845e589b71 to the isolated MiniApp and Skin market services after verifying daily backups and restore drills. Both containers are healthy and their public health endpoints pass. Sample compact payloads are approximately 74% smaller for MiniApp and 73% smaller for Skin.