IAV-260/Refactor: Simplify notification config to one-to-one and scope FAQ categories per agent

Summary

This MR refactors entity relationships for AgentNotificationConfig and FaqCategory to better align with business requirements.

Changes

1. AgentNotificationConfig - One-to-One Relationship

• Before: @ManyToOne - An agent could have multiple notification configs
• After: @OneToOne - Each agent has exactly one notification configuration

2. CustomerCareAgent Updates

• Changed notificationConfigs (List) → notificationConfig (single entity)
• Removed integrations relationship (AgentIntegration)

3. FaqCategory - Per-Agent Scoping

• Added customerCareAgent foreign key relationship
• Removed unique constraint on name column
• FAQ categories are now scoped per agent, allowing different agents to have categories with the same name

Breaking Changes

• CustomerCareAgent.getNotificationConfigs() → getNotificationConfig()
• CustomerCareAgent.getIntegrations() removed
• FaqCategory now requires a CustomerCareAgent reference

Closes IAV-260