Add error page

proxy/web/src/data.ts

@@ -1,9 +1,21 @@
 // Auth method types matching Go
 export type AuthMethod = 'pin' | 'password' | 'oidc' | "link"
 
+// Page types
+export type PageType = 'auth' | 'error'
+
+// Error data structure
+export interface ErrorData {
+  code: number
+  title: string
+  message: string
+}
+
 // Data injected by Go templates
 export interface Data {
+  page?: PageType
   methods?: Partial<Record<AuthMethod, string>>
+  error?: ErrorData
 }
 
 declare global {