Initial fullstack project setup with Next.js 15, Gin, PostgreSQL and Docker Compose

- Frontend: Next.js 15 (App Router), Auth.js v5, shadcn/ui, MagicUI
- Backend: Go + Gin + GORM with layered architecture
- Auth: Local credentials login with optional Keycloak OAuth binding
- Admin: RBAC user management for admin role
- Dev: Docker Compose with hot reload for both frontend and backend
- Docker: 3-service orchestration (frontend, backend, postgres)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/db/db.go

@@ -0,0 +1,27 @@
+package db
+
+import (
+	"log"
+
+	"evanpage-backend/internal/config"
+	"evanpage-backend/internal/domain"
+	"gorm.io/driver/postgres"
+	"gorm.io/gorm"
+)
+
+var DB *gorm.DB
+
+func Init(cfg *config.Config) *gorm.DB {
+	var err error
+	DB, err = gorm.Open(postgres.Open(cfg.DatabaseURL), &gorm.Config{})
+	if err != nil {
+		log.Fatalf("failed to connect database: %v", err)
+	}
+
+	if err := DB.AutoMigrate(&domain.User{}); err != nil {
+		log.Fatalf("failed to migrate database: %v", err)
+	}
+
+	log.Println("database connected and migrated")
+	return DB
+}