chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

backend/cmd/api/main.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"os"
+
+	db "github.com/chedius/delivery-tracker/internal/db/sqlc"
+	"github.com/chedius/delivery-tracker/internal/delivery"
+	"github.com/gin-gonic/gin"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/joho/godotenv"
+)
+
+func main() {
+	ctx := context.Background()
+	godotenv.Load()
+
+	dsn := os.Getenv("DATABASE_URL")
+	pool, err := pgxpool.New(ctx, dsn)
+	if err != nil {
+		log.Fatalf("db connect: %v", err)
+	}
+	defer pool.Close()
+
+	queries := db.New(pool)
+	h := delivery.NewHandler(queries)
+
+	r := gin.Default()
+
+	r.GET("/health", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	})
+
+	r.GET("/api/deliveries", h.GetDeliveries)
+	r.GET("/api/deliveries/:id", h.GetDeliveryByID)
+	r.POST("/api/deliveries", h.CreateDelivery)
+	r.PATCH("/api/deliveries/:id", h.UpdateDelivery)
+	r.DELETE("/api/deliveries/:id", h.DeleteDelivery)
+
+	r.Run(":8080")
+}