Move sendEmail to dedicated file for better visibility

- Extract sendEmail function to src/sendEmail.ts as primary module
- Export BaseEmailData and SendEmailOptions interfaces alongside
- Update all imports to use new location
- Add sendEmailDefault export for CommonJS compatibility
- Export parseAndValidateEmails for external utility use
- Updated README to highlight sendEmail as primary export

Breaking change: BaseEmailData and SendEmailOptions now imported from main module, not utils/helpers

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

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

src/index.ts

@@ -15,13 +15,15 @@ export { default as Emails } from './collections/Emails.js'
 export { mailingJobs, sendEmailJob } from './jobs/index.js'
 export type { SendEmailTaskInput } from './jobs/sendEmailTask.js'
 
+// Main email sending function
+export { sendEmail, type BaseEmailData, type SendEmailOptions } from './sendEmail.js'
+export { default as sendEmailDefault } from './sendEmail.js'
+
 // Utility functions for developers
 export {
   getMailing,
   renderTemplate,
   processEmails,
   retryFailedEmails,
-  sendEmail,
-  type BaseEmailData,
-  type SendEmailOptions,
+  parseAndValidateEmails,
 } from './utils/helpers.js'