v0.4.0

Added

• C API: new ctt-c-api crate produces static/dynamic libraries plus a hand-curated ctt.h header. Signed, attested prebuilt archives are published for Windows, macOS, and Linux on x86_64 and aarch64.
• 3D (volume) texture support end-to-end: load/encode/store 3D textures via DDS and KTX2. New CLI --volume flag stacks input files as Z slices.
• AVX-512 sRGB load/store kernels (x86_64) and NEON sRGB load/store kernels (aarch64), selected at runtime.
• Bulk f16 ↔ f32 processing kernels.
• Per-encoder option flags: --astcenc-opts, --bc7e-opts, --intel-opts, --etcpak-opts, --amd-opts accept key=val[;key=val...] strings. --help-encoder <name> lists available keys with types and docs.
• Substantially expanded astcenc settings: usage modes (Color, NormalMap with Bc5Compat/AstcDefault swizzle, SingleChannel, TwoChannel, HdrRgb, HdrRgba, Rgbm), perceptual mode, alpha-weighted error, decode_unorm8 tuning, RGBM scale, custom preset override.
• CLI integration test suite covering color/alpha conversion, containers, cubemaps, cubemap arrays, mipmaps, volumes, swizzle, supercompression, passthrough, and error paths.

Changed

• API: TargetFormat::Compressed now carries a typed encoder: Encoder enum (with per-backend settings) instead of encoder_name: Option<String>. Use Encoder::Auto for "any encoder that supports this format".
• API: parse_format signature is now parse_format(&str) -> Result<TargetFormat> — the EncoderRegistry parameter is gone; compiled-in encoders are discovered statically.
• API: Image::is_cubemap: bool replaced with Image::kind: TextureKind (Texture2D / Cubemap / Texture3D).
• API: Surface gains depth and slice_stride fields for 3D surfaces (set depth = 1, slice_stride = 0 for 2D).
• CLI --help output wraps to the terminal width.
• ASTC encoder defaults tuned for better quality out of the box.
• Passthrough path widened — more input/output combinations skip re-encoding.

Fixed

• ctt-compressonator now builds on older GCC versions.