feat: add GORM integration with repository pattern

- Add GORM models in models/ directory with proper column tags
- Create repository interfaces and implementations in core/repository/
- Add database package with MySQL and SQLite support
- Add UUID ID utility for GORM models
- Implement complete repository layer replacing SQL-based data access
- Add database migrations and index creation
- Support both MySQL and SQLite drivers with auto-migration

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

models/split.go

@@ -0,0 +1,17 @@
+package models
+
+// Split represents a single entry in a transaction
+type Split struct {
+	ID            uint   `gorm:"primaryKey;autoIncrement"`
+	TransactionID []byte `gorm:"column:transactionId;type:BINARY(16);not null"`
+	AccountID     []byte `gorm:"column:accountId;type:BINARY(16);not null"`
+	Date          uint64 `gorm:"column:date;not null"`
+	Inserted      uint64 `gorm:"column:inserted;not null"`
+	Updated       uint64 `gorm:"column:updated;not null"`
+	Amount        int64  `gorm:"column:amount;not null"`
+	NativeAmount  int64  `gorm:"column:nativeAmount;not null"`
+	Deleted       bool   `gorm:"column:deleted;default:false"`
+
+	Transaction Transaction `gorm:"foreignKey:TransactionID"`
+	Account     Account     `gorm:"foreignKey:AccountID"`
+}