SDK beta.62: fix dynamicSelect crash on empty values, add smtpShape

- Guard z.union() against empty arrays in dynamicSelect/dynamicMultiselect
  by falling back to z.string() (fixes zod v4 _zod TypeError)
- Add smtpShape: typed zod schema for store file models, replacing
  smtpInputSpec.validator which caused cross-zod-instance errors
- Bump version to 0.4.0-beta.62

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sdk/package/lib/StartSdk.ts

@@ -11,6 +11,7 @@ import * as patterns from '../../base/lib/util/patterns'
 import { Backups } from './backup/Backups'
 import {
   smtpInputSpec,
+  smtpShape,
   systemSmtpSpec,
   customSmtp,
   smtpProviderVariants,
@@ -408,6 +409,7 @@ export class StartSdk<Manifest extends T.SDKManifest> {
       },
       inputSpecConstants: {
         smtpInputSpec,
+        smtpShape,
         systemSmtpSpec,
         customSmtp,
         smtpProviderVariants,