IAV-1044/fix(credential): correct WHATSAPP_OAUTH N8N type mapping

What

Fixes incorrect bidirectional mapping for WHATSAPP_OAUTH credential type.

Why

• Previous logic used contains("oauth") to detect WhatsApp OAuth, causing false positives with other OAuth-based types
• The N8N type was set to whatsAppOAuthApi which does not exist — correct value is whatsAppTriggerApi

Changes

• mapN8NTypeToCredentialType: detection condition updated (trigger instead of oauth)
• mapCredentialTypeToN8NType: WHATSAPP_OAUTH → whatsAppTriggerApi

Related Issues

Closes IAV-1044