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/app/update.rs

@@ -49,6 +49,7 @@ impl H7CAD {
                 self.tabs[i].current_path = Some(path);
                 self.tabs[i].scene.document = doc;
                 self.tabs[i].scene.populate_hatches_from_document();
+                self.tabs[i].scene.populate_images_from_document();
                 self.tabs[i].scene.selected = std::collections::HashSet::new();
                 self.tabs[i].scene.preview_wires = vec![];
                 self.tabs[i].scene.current_layout = "Model".to_string();
@@ -71,6 +72,35 @@ impl H7CAD {
                 Task::none()
             }
 
+            Message::ImagePick => {
+                Task::perform(crate::io::pick_image_file(), Message::ImagePickResult)
+            }
+
+            Message::ImagePickResult(Ok((path, pw, ph))) => {
+                use crate::command::CadCommand;
+                use crate::modules::home::draw::raster_image::ImageCommand;
+                let path_str = path.to_string_lossy().into_owned();
+                let short = std::path::Path::new(&path_str)
+                    .file_name()
+                    .and_then(|n| n.to_str())
+                    .unwrap_or(&path_str)
+                    .to_string();
+                self.command_line
+                    .push_output(&format!("IMAGE  \"{short}\": {pw}×{ph} px"));
+                let cmd = ImageCommand::new(path_str, pw, ph);
+                let i = self.active_tab;
+                self.command_line.push_info(&cmd.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(cmd));
+                Task::none()
+            }
+
+            Message::ImagePickResult(Err(e)) => {
+                if e != "Cancelled" {
+                    self.command_line.push_error(&format!("IMAGE: {e}"));
+                }
+                Task::none()
+            }
+
             Message::SaveFile => {
                 let i = self.active_tab;
                 if let Some(path) = &self.tabs[i].current_path {