Step 3 prep: Domain renders at 1.0, add scroll_id to model

src/ui/model.rs

@@ -112,6 +112,7 @@ pub struct AppModel {
     pub scale: f32,
     pub canvas_size: Size,
     pub image_size: Size,
+    pub scroll_id: cosmic::widget::Id,
 
     // Tool state
     pub tool_mode: ToolMode,
@@ -150,6 +151,7 @@ impl AppModel {
             scale: 1.0,
             canvas_size: Size::ZERO,
             image_size: Size::ZERO,
+            scroll_id: cosmic::widget::Id::new("canvas-scroll"),
             // Tool state
             tool_mode: ToolMode::None,
             crop_selection: CropSelection::default(),

src/ui/sync.rs

@@ -52,7 +52,7 @@ pub fn sync_model_from_manager(model: &mut AppModel, manager: &mut DocumentManag
 pub fn sync_render_data(model: &mut AppModel, manager: &mut DocumentManager) {
     if let Some(doc) = manager.current_document_mut() {
         // Re-render at current scale to get updated image handle
-        if let Ok(render_output) = doc.render(model.scale as f64) {
+        if let Ok(render_output) = doc.render(1.0) {
             model.current_image_handle = Some(render_output.handle);
         }