IAV-848/refactor(customer-care): decouple integration entity from n8n and scope supported integration types

Summary

This MR refactors the customer care integration layer to make it more generic and maintainable, decoupling it from n8n implementation details.

Changes

Entity — CustomerCareAgentIntegration (formerly AgentIntegration)

• Renamed class and DB table to align with the CustomerCare module naming convention
• Removed n8n-specific fields (n8nWorkflowId, n8nWorkflowName, n8nWebhookUrl) — the integration entity no longer carries workflow orchestration details
• Replaced with two UID references:
  • userIntegrationUid — links to the user-level integration configuration
  • credentialInstanceUid — links to the credential instance used by this integration
• Removed available flag — availability is now an implicit concern of the referenced credential/integration, not stored redundantly here

IntegrationType enum

• Scoped down to only the channels and systems currently supported
• Renamed INSTAGRAM → INSTAGRAM_HEADER_AUTH to make the auth strategy explicit and match the corresponding CredentialType
• Removed prematurely added types: DISCORD, SLACK, LINKEDIN, TIKTOK, YOUTUBE, TWITTER, ZENDESK, JIRA_SERVICE_MANAGEMENT, HUBSPOT_CRM

CredentialType enum

• Added INSTAGRAM_HEADER_AUTH to align with the renamed IntegrationType value

Related Issues

Closes IAV-848