feat: add Docker deployment and application configuration

Add package declarations across the Go scaffold, YAML configuration loading and validation, and a minimal API entry point.

Add development and production Compose files, a multi-stage Docker image, configuration template, and Make targets. Remove the directory scaffolding script.

cmd/api/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"log"
+
+	"git.my-rm.com/Robot-Market/shop-backend/internal/app"
+)
+
+func main() {
+	if _, err := app.LoadConfig(""); err != nil {
+		log.Fatal(err)
+	}
+}