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/token.go

@@ -0,0 +1,10 @@
+package models
+
+// Token represents an API token
+type Token struct {
+	ID        []byte `gorm:"type:BINARY(16);primaryKey"`
+	Name      string `gorm:"column:name;size:100"`
+	UserOrgID uint   `gorm:"column:userOrgId;not null"`
+
+	UserOrg UserOrg `gorm:"foreignKey:UserOrgID"`
+}