feat: migrate store layer to GORM with PostgreSQL support

- Migrate all store packages from raw database/sql to GORM ORM
- Add PostgreSQL support alongside SQLite
- Move EncryptedString type to crypto package for cleaner architecture
- Add automatic encryption/decryption for sensitive fields (API keys, secrets)
- Fix PostgreSQL AutoMigrate conflicts by skipping existing tables
- Fix duplicate /klines route registration
- Update tests to use GORM database connections
- Add database configuration support in config package

store/gorm.go

@@ -0,0 +1,146 @@
+package store
+
+import (
+	"fmt"
+
+	"gorm.io/driver/postgres"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+// GormDB is the global GORM database connection
+var gormDB *gorm.DB
+
+// DB returns the GORM database connection
+func DB() *gorm.DB {
+	return gormDB
+}
+
+// InitGorm initializes GORM with SQLite
+func InitGorm(dbPath string) (*gorm.DB, error) {
+	db, err := gorm.Open(sqlite.Open(dbPath), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to open SQLite database: %w", err)
+	}
+
+	// Set connection pool for SQLite
+	sqlDB, err := db.DB()
+	if err != nil {
+		return nil, err
+	}
+	sqlDB.SetMaxOpenConns(1)
+	sqlDB.SetMaxIdleConns(1)
+
+	// Enable foreign keys for SQLite
+	db.Exec("PRAGMA foreign_keys = ON")
+	db.Exec("PRAGMA journal_mode = DELETE")
+	db.Exec("PRAGMA synchronous = FULL")
+	db.Exec("PRAGMA busy_timeout = 5000")
+
+	gormDB = db
+	return db, nil
+}
+
+// InitGormPostgres initializes GORM with PostgreSQL
+func InitGormPostgres(host string, port int, user, password, dbname, sslmode string) (*gorm.DB, error) {
+	dsn := fmt.Sprintf(
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
+		host, port, user, password, dbname, sslmode,
+	)
+
+	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to open PostgreSQL database: %w", err)
+	}
+
+	// Set connection pool for PostgreSQL
+	sqlDB, err := db.DB()
+	if err != nil {
+		return nil, err
+	}
+	sqlDB.SetMaxOpenConns(25)
+	sqlDB.SetMaxIdleConns(5)
+
+	gormDB = db
+	return db, nil
+}
+
+// InitGormWithConfig initializes GORM with provided configuration
+// Uses DBConfig from driver.go
+func InitGormWithConfig(cfg DBConfig) (*gorm.DB, error) {
+	switch cfg.Type {
+	case DBTypeSQLite:
+		return InitGorm(cfg.Path)
+
+	case DBTypePostgres:
+		return InitGormPostgres(
+			cfg.Host,
+			cfg.Port,
+			cfg.User,
+			cfg.Password,
+			cfg.DBName,
+			cfg.SSLMode,
+		)
+
+	default:
+		return nil, fmt.Errorf("unsupported DB_TYPE: %s (use 'sqlite' or 'postgres')", cfg.Type)
+	}
+}
+
+// ============================================================================
+// Query Scopes - Reusable query helpers
+// ============================================================================
+
+// ForUser returns a scope that filters by user_id
+func ForUser(userID string) func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Where("user_id = ?", userID)
+	}
+}
+
+// ForTrader returns a scope that filters by trader_id
+func ForTrader(traderID string) func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Where("trader_id = ?", traderID)
+	}
+}
+
+// OpenPositions returns a scope for open positions
+func OpenPositions() func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Where("status = ?", "OPEN")
+	}
+}
+
+// ClosedPositions returns a scope for closed positions
+func ClosedPositions() func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Where("status = ?", "CLOSED")
+	}
+}
+
+// OrderByCreatedDesc returns a scope that orders by created_at DESC
+func OrderByCreatedDesc() func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Order("created_at DESC")
+	}
+}
+
+// OrderByUpdatedDesc returns a scope that orders by updated_at DESC
+func OrderByUpdatedDesc() func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Order("updated_at DESC")
+	}
+}
+
+// Paginate returns a scope for pagination
+func Paginate(limit, offset int) func(*gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Limit(limit).Offset(offset)
+	}
+}