feat: raster image render pipeline (IMAGE command + GPU textured quad)

- Add IMAGE / IMAGEATTACH / IM command with async file-picker (rfd)
- src/scene/image_model.rs: ImageModel with RGBA pixel data + quad corners
- src/scene/pipeline/image_gpu.rs: ImageGpu with wgpu texture, sampler, opacity uniform
- src/scene/pipeline/mod.rs: image render pipeline (pass 2, between hatches and meshes)
- src/scene/render.rs: include images in Primitive, call upload_images in prepare
- src/scene/mod.rs: images HashMap, populate_images_from_document, cache on add_entity
- src/modules/home/draw/raster_image.rs: ImageCommand (two-click: origin + width, aspect-correct preview)
- src/io/mod.rs: pick_image_file() async helper (file dialog + dimension decode)
- app: ImagePick / ImagePickResult messages, populate on file open and undo/redo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/layout/mview.rs

@@ -95,6 +95,7 @@ impl CadCommand for MviewCommand {
             line_weight_px: 1.0,
             snap_pts: vec![],
             tangent_geoms: vec![],
+            aci: 0,
             key_vertices: vec![],
         })
     }