Add service communication via OpenFeign

[MordechaiDavid]

Description:
Setup communication with existing MediSync services using OpenFeign clients.

Acceptance Criteria:

• Create Feign clients for auth-service, patient-service, doctor-service
• Configure load balancing with Eureka
• Add JWT token propagation
• Implement circuit breaker patterns
• Add proper error handling for service calls
• Register with Eureka discovery