fix: Resolve TypeScript type error and Docker warning

- Make createUser field required in FormData interface to match yup schema
- Add explicit optional handling for username/password in yup schema
- Fix Docker FROM casing warning (as -> AS)
- Ensure TypeScript compilation passes without errors

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docker/Dockerfile.frontend

@@ -1,5 +1,5 @@
 # Build stage
-FROM node:20-alpine as builder
+FROM node:20-alpine AS builder
 
 WORKDIR /app
 

frontend/src/components/Buckets/CreateBucketDialog.tsx

@@ -35,7 +35,7 @@ interface CreateBucketDialogProps {
 
 interface FormData {
   bucketName: string;
-  createUser?: boolean;
+  createUser: boolean;
   username?: string;
   password?: string;
 }
@@ -50,7 +50,7 @@ const schema = yup.object({
     )
     .min(3, 'Minimum 3 characters')
     .max(63, 'Maximum 63 characters'),
-  createUser: yup.boolean().default(true),
+  createUser: yup.boolean().defined().default(true),
   username: yup
     .string()
     .when('createUser', {
@@ -64,6 +64,7 @@ const schema = yup.object({
           )
           .min(3, 'Minimum 3 characters')
           .max(32, 'Maximum 32 characters'),
+      otherwise: (schema) => schema.optional(),
     }),
   password: yup
     .string()
@@ -77,6 +78,7 @@ const schema = yup.object({
             /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)/,
             'Password must contain uppercase, lowercase, and number'
           ),
+      otherwise: (schema) => schema.optional(),
     }),
 });