Add NIP-95 upload endpoint documentation and improve error message

- Add NEXT_PUBLIC_NIP95_UPLOAD_URL to README environment variables section
- Add NIP-95 upload service documentation with examples
- Create .env.example file with all required environment variables
- Improve error message to guide users to README for setup instructions
- All TypeScript checks pass

components/PresentationFormHeader.tsx

@@ -19,4 +19,3 @@ export function PresentationFormHeader({ userName }: PresentationFormHeaderProps
     </div>
   )
 }
-

lib/nip95.ts

@@ -38,7 +38,9 @@ export async function uploadNip95Media(file: File): Promise<MediaRef> {
 
   const endpoint = process.env.NEXT_PUBLIC_NIP95_UPLOAD_URL
   if (!endpoint) {
-    throw new Error('NIP-95 upload endpoint is not configured')
+    throw new Error(
+      'NIP-95 upload endpoint is not configured. Please set NEXT_PUBLIC_NIP95_UPLOAD_URL environment variable. See README.md for setup instructions.'
+    )
   }
 
   const formData = new FormData()