core: initial Go module skeleton (config, db pool, tenant registry migration)

cmd/core/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"context"
+	"log"
+	"net/http"
+
+	"gitea.perlbach24.de/scripte/nexarch/internal/config"
+	"gitea.perlbach24.de/scripte/nexarch/internal/db"
+)
+
+func main() {
+	cfg, err := config.Load()
+	if err != nil {
+		log.Fatalf("config: %v", err)
+	}
+
+	pool, err := db.Connect(context.Background(), cfg.RegistryDSN)
+	if err != nil {
+		log.Fatalf("db: %v", err)
+	}
+	defer pool.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+
+	log.Printf("nexarch-core listening on %s", cfg.ListenAddr)
+	if err := http.ListenAndServe(cfg.ListenAddr, mux); err != nil {
+		log.Fatalf("server: %v", err)
+	}
+}