fix: unify image quality behavior and docs

[mrousavy]

Summary

• correct inaccurate image data and API documentation
• standardize image quality on 0...100 with a default of 100 on Android and iOS
• validate before conversion and round fractional quality to the nearest integer on both platforms
• add shared harness coverage for endpoints, defaults, rounding, sync errors, and async rejections

Validation

• bun run lint-ci
• bun run build
• bun run typecheck
• bunx tsc -p example/tsconfig.json --noEmit
• Nitrogen codegen (6/6 specs)
• Android release Kotlin compilation
• iOS simulator Debug build