docs: Fix incorrect code examples in TypeScript support documentation

[wo-o29]

Summary

This PR fixes three code errors in the TypeScript support documentation:

1. SubmitErrorHandler example: Fixed incorrect register() usage where the return value wasn't being spread properly due to comma operator misuse
2. NestedValue example: Removed duplicate Autocomplete import from @material-ui/core (it only exists in @material-ui/lab)
3. NestedValue example: Fixed field name mismatch where setValue("muiSelect", ...) was used but the form type only defines a select field

Changes

• Fixed register spread syntax from {...(register("firstName"), { required: true })} to {...register("firstName", { required: true })}
• Removed duplicate Autocomplete import from @material-ui/core
• Changed setValue("muiSelect", ...) to setValue("select", ...)

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