feat(imaging): add pure-Rust Skia backend (#112)

docs/imaging-meshing.md

@@ -18,7 +18,8 @@ and [`MeshFoundry` guide](../crates/libremetaverse-rendering-mesh-foundry/README
 | Managed images and TGA | enabled | n/a | none |
 | JPEG 2000 | disabled | `libremetaverse-imaging/jpeg2000` | OpenJPEG 2.5.x |
 | JPEG 2000 (pure Rust) | disabled | `libremetaverse-imaging/rust-j2k` | none (`j2k` 0.8.1) |
-| BMP/GIF/ICO/JPEG/PNG/WBMP/WebP | disabled | `libremetaverse-imaging-skia/skia` | Skia |
+| BMP/GIF/ICO/JPEG/PNG/WBMP/WebP (pure Rust) | disabled | `libremetaverse-imaging-skia/rust-skia` | none (`skia-rs-codec` 0.3.0 plus `image-webp` 0.2.4) |
+| BMP/GIF/ICO/JPEG/PNG/WBMP/WebP (native) | disabled | `libremetaverse-imaging-skia/skia` | Skia |
 | Prim and sculpt meshing, OBJ ingestion | enabled | n/a | none |
 
 OpenJPEG is a non-default workspace member so release tooling can package the
@@ -26,10 +27,11 @@ adapter explicitly, and imaging reaches it only through the optional
 dependency. The independent `rust-j2k` feature reaches only the audited
 pure-Rust `j2k` graph; enabling both features keeps both explicit codec types
 available for interoperability testing. Skia is likewise an optional,
-target-specific dependency. The
-consolidated required Gitea gate exercises both optional features on
-`ubuntu-latest` while its minimal-feature check proves that no native codec is
-needed for the owned Rust and translated compatibility tests.
+target-specific dependency. The consolidated required Gitea gate exercises the
+native feature, while a dedicated `ubuntu-latest` job tests `rust-skia`, audits
+its normal/build graph without installing native codec tools, and compiles the
+same code for WASM. Minimal-feature checks still prove no codec is needed for
+the owned Rust and translated compatibility tests.
 
 ## Bounds and rendering contract