klearu-image CLI does not propagate diffusion image-io feature

[blacks1ne]

Summary

klearu-image's CLI feature does not enable the downstream diffusion image-I/O feature required by img_sample's Rust PNG path.

Evidence

• img_sample calls klearu_diffusion::image_io::save_png.
• The working save_png implementation is gated by klearu-diffusion/image-io; otherwise a runtime fallback always returns an unsupported-feature error.
• klearu-image currently defines cli = ["dep:image"] but does not include klearu-diffusion/image-io.

The binary can compile while retaining a PNG path that always fails at runtime in a package-only build.

Proposed resolution

• Change the feature to propagate klearu-diffusion/image-io.
• Add required-features = ["cli"] to binaries that actually require image I/O.
• Remove a redundant direct image dependency if it is not otherwise used.

Acceptance criteria

• A package-only cargo run -p klearu-image --features cli --bin img_sample ... can write a PNG.
• A small feature-gated test exercises PNG encode/read behavior.
• Building without cli either omits the binary or reports the requirement at build time rather than late runtime.