Fix canvas initialization and sizing bugs

- Add image loading validation before sending canvas data to server
  Prevents 'Failed to get confirmation' error when images haven't
  finished loading after workflow reload. Waits 100ms and checks
  if all layer images are complete before rendering output.

- Improve layer loading error handling in CanvasState
  Better logging when layers fail to load from IndexedDB.
  Allows empty canvas as valid state instead of failing.

- Add ResizeObserver for canvas container
  Fixes bug where canvas only shows in top half of node.
  Watches container size changes and triggers re-render to ensure
  canvas dimensions are correctly calculated after DOM layout.

js/CanvasIO.js

@@ -197,6 +197,18 @@ export class CanvasIO {
     }
     async _renderOutputData() {
         log.info("=== RENDERING OUTPUT DATA FOR COMFYUI ===");
+        // Check if layers have valid images loaded
+        const layersWithoutImages = this.canvas.layers.filter(layer => !layer.image || !layer.image.complete);
+        if (layersWithoutImages.length > 0) {
+            log.warn(`${layersWithoutImages.length} layer(s) have incomplete image data. Waiting for images to load...`);
+            // Wait a bit for images to load
+            await new Promise(resolve => setTimeout(resolve, 100));
+            // Check again
+            const stillIncomplete = this.canvas.layers.filter(layer => !layer.image || !layer.image.complete);
+            if (stillIncomplete.length > 0) {
+                throw new Error(`Canvas not ready: ${stillIncomplete.length} layer(s) still have incomplete image data. Try clicking on a layer to force initialization, or wait a moment and try again.`);
+            }
+        }
         // Użyj zunifikowanych funkcji z CanvasLayers
         const imageBlob = await this.canvas.canvasLayers.getFlattenedCanvasAsBlob();
         const maskBlob = await this.canvas.canvasLayers.getFlattenedMaskAsBlob();