- Add Database struct with GORM PostgreSQL connection
- Add IMSIAllocation model for IMSI range tracking and allocation
- Add NewDatabase function with connection pooling (10 idle, 100 max connections, 1h lifetime)
- Add AutoMigrate for Subscriber, ServicePlan, Session, UsageRecord, and IMSIAllocation models
- Add InitializeIMSIAllocation with default IMSI range (1-999999999)
- Add CRUD operations for subscribers (Create, Get, GetByIMSI, Update, List)
- Add ListSubscribers with pagination, filtering by status/
- Add Config struct with server, database, Redis, IMSI, and ES2+ settings
- Add ServerConfig with port and timeout settings (30s read/write)
- Add DatabaseConfig for PostgreSQL connection parameters
- Add RedisConfig for cache connection settings
- Add IMSIConfig with France MCC+MNC prefix (20893) and IMSI range
- Add ES2Config for eSIM provisioning with SMDP connection parameters
- Add LoadConfig function with default configuration values
- Include JSON
nutcas3