Fix code review issues - replace deprecated substr() and remove type assertions

Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

Author: Copilot

apps/playground/src/pages/Studio.tsx

@@ -244,7 +244,7 @@ const StudioToolbarContext = ({
 
 // Inner Component handles state for a specific example
 const StudioEditor = ({ exampleId, initialJson, isUserDesign, currentDesignId }: { 
-  exampleId: ExampleKey | 'new', 
+  exampleId: ExampleKey | 'new' | string, 
   initialJson: string,
   isUserDesign?: boolean,
   currentDesignId?: string
@@ -608,7 +608,7 @@ export const Studio = () => {
     return (
       <StudioEditor 
         key={userDesign.id} 
-        exampleId={userDesign.id as any} 
+        exampleId={userDesign.id} 
         initialJson={initialCode}
         isUserDesign={true}
         currentDesignId={userDesign.id}
@@ -622,7 +622,7 @@ export const Studio = () => {
     const sharedDesign = designStorage.getSharedDesign(shareId);
     if (sharedDesign) {
       const initialCode = JSON.stringify(sharedDesign.schema, null, 2);
-      return <StudioEditor key={shareId} exampleId={sharedDesign.name as any} initialJson={initialCode} />;
+      return <StudioEditor key={shareId} exampleId={sharedDesign.name} initialJson={initialCode} />;
     }
   }
 

apps/playground/src/services/designStorage.ts

@@ -156,11 +156,11 @@ class DesignStorageService {
 
   // Private helper methods
   private generateId(): string {
-    return `design_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
+    return `design_${Date.now()}_${Math.random().toString(36).substring(2, 11)}`;
   }
 
   private generateShareId(): string {
-    return Math.random().toString(36).substr(2, 12);
+    return Math.random().toString(36).substring(2, 14);
   }
 
   private getSharedDesigns(): Record<string, Design> {