Method validateUniqueName

src/api/pdf-form.ts:1105–1109

* Validate that a field name is unique.

(name: string)

   * Validate that a field name is unique.
   */
  private validateUniqueName(name: string): void {
    if (this.fieldsByName.has(name)) {
      throw new Error(`Field "${name}" already exists`);
    }
  }

  /**
   * Build a default appearance (DA) string for text-based fields.