feat(imaging): default to pure-Rust codecs

crates/libremetaverse-imaging-skia/README.md

@@ -6,7 +6,8 @@ exposes a `skia-safe` type and never discovers or links Skia.
 
 ## Features and formats
 
-The default feature set has no Skia dependency. `SkiaTextureCodec::decode` and
+The default feature set enables the pure-Rust `rust-skia` backend and has no
+native Google Skia dependency. `SkiaTextureCodec::decode` and
 `RustSkiaTextureCodec::decode` return a typed `InvalidOperation` error when
 their respective feature is disabled, while conversion from the checked
 project-owned `backend::SKBitmap` remains available for tests and callers that
@@ -15,7 +16,7 @@ already own decoded pixels.
 For a fully Rust implementation, enable:
 
 ```sh
-cargo test -p libremetaverse-imaging-skia --no-default-features --features rust-skia
+cargo test -p libremetaverse-imaging-skia
 ```
 
 `rust-skia` pins [`skia-rs-codec` 0.3.0](https://github.com/rust-skia/skia-rs)