fix: wrap default object literals in parentheses

[phall1]

Problem

When a schema has "default": {}, the generated TypeScript code was:

default: () => {} as const

This is invalid JavaScript/TypeScript because {} after an arrow is parsed as an empty block statement (returning undefined), not an object literal.

Solution

Wrap the JSON.stringify output in parentheses:

default: () => ({} as const)

Example

OpenAPI schema:

{
  "task_status_counts": {
    "type": "object",
    "additionalProperties": { "type": "integer" },
    "default": {}
  }
}

Before (invalid):

S.optionalWith(S.Record(...), { nullable: true, default: () => {} as const })

After (valid):

S.optionalWith(S.Record(...), { nullable: true, default: () => ({} as const) })