feat: enhance canvas functionality with new asset node type and improved image handling

- Introduced a new "asset" node type in the canvas sidebar for better resource management.
- Updated image node components to support dynamic image dimensions and improved resizing logic.
- Enhanced prompt and AI image nodes to utilize reference images from asset nodes, improving integration and functionality.
- Refactored canvas utilities to accommodate new asset configurations and maintain consistent media handling.

components/canvas/canvas-sidebar.tsx

@@ -2,6 +2,7 @@
 
 const nodeTemplates = [
   { type: "image", label: "Bild", icon: "🖼️", category: "Quelle" },
+  { type: "asset", label: "Asset", icon: "🛍️", category: "Quelle" },
   { type: "text", label: "Text", icon: "📝", category: "Quelle" },
   { type: "prompt", label: "Prompt", icon: "✨", category: "Quelle" },
   { type: "note", label: "Notiz", icon: "📌", category: "Layout" },