feat: add design persistence functionality with Auth0 and Supabase integration

- Implemented `useDesignPersistence` composable for managing design records.
- Enhanced `useSlipmatDesigner` to support loading designs from JSON.
- Created global authentication middleware for route protection.
- Added Supabase client plugin for database interactions.
- Developed API endpoints for fetching, saving, and retrieving designs.
- Introduced utility functions for Auth0 token verification and Supabase client retrieval.
- Updated Nuxt configuration to include Auth0 and Supabase environment variables.
- Added necessary dependencies for Auth0 and Supabase.
- Enhanced TypeScript configuration for improved type support.

composables/useSlipmatDesigner.ts

@@ -20,6 +20,7 @@ export interface ExportedDesign {
   productionBlob: Blob;
   templateId: string;
   createdAt: string;
+  canvasJson: FabricCanvasJSON;
 }
 
 const DISPLAY_SIZE = 720;
@@ -63,6 +64,7 @@ type FabricCircle = FabricNamespace.Circle;
 type FabricRect = FabricNamespace.Rect;
 type FabricTextbox = FabricNamespace.Textbox;
 type FabricObject = FabricNamespace.Object;
+type FabricCanvasJSON = ReturnType<FabricCanvas["toJSON"]>;
 
 type CanvasReadyPayload = {
   canvas: FabricCanvas;
@@ -638,6 +640,8 @@ export const useSlipmatDesigner = () => {
       }
       productionObjectUrl.value = URL.createObjectURL(productionDataBlob);
 
+      const canvasJson = currentCanvas.toJSON() as FabricCanvasJSON;
+
       return {
         previewUrl: previewDataUrl,
         previewBlob: previewDataBlob,
@@ -645,12 +649,30 @@ export const useSlipmatDesigner = () => {
         productionBlob: productionDataBlob,
         templateId: selectedTemplate.value.id,
         createdAt: new Date().toISOString(),
+        canvasJson,
       };
     } finally {
       isExporting.value = false;
     }
   };
 
+  const loadDesignFromJson = async (designJson: FabricCanvasJSON) => {
+    const fabric = fabricApi.value;
+    const currentCanvas = canvas.value;
+    if (!fabric || !currentCanvas) {
+      return;
+    }
+
+    await new Promise<void>((resolve) => {
+      currentCanvas.loadFromJSON(designJson, () => {
+        currentCanvas.renderAll();
+        maintainStaticLayerOrder();
+        schedulePreviewRefresh();
+        resolve();
+      });
+    });
+  };
+
   const downloadPreview = async () => {
     if (!previewUrl.value) {
       await refreshPreview();
@@ -717,6 +739,7 @@ export const useSlipmatDesigner = () => {
     resetZoom,
     clearDesign,
     exportDesign,
+  loadDesignFromJson,
     downloadPreview,
     downloadProduction,
     refreshPreview,