feat: add server foundation (config, database, auth, main)

- config: Load from env vars (SERVER_PORT, DATABASE_URL, JWT_SECRET, CAS_DIR, etc.)
- database: pgx/v5 connection pool, models (User, YggdrasilSession, Modpack, GlobalFile, LauncherRelease)
- auth: Yggdrasil endpoints (authenticate, refresh, validate) with SHA-256 password hashing, token rotation
- main: graceful shutdown, HTTP server on configured port
- go.mod: module gitea.mrixs.me/Mrixs/MrixsCraft-server, pgx/v5 dependency

Co-Authored-By: OWL <noreply@anthropic.com>

cmd/server/main.go

@@ -1,26 +1,77 @@
 package main
 
 import (
-	"fmt"
+	"context"
 	"log"
 	"net/http"
 	"os"
+	"os/signal"
+	"strconv"
+	"syscall"
+	"time"
+
+	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/auth"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/config"
+	"gitea.mrixs.me/Mrixs/MrixsCraft-server/internal/database"
 )
 
 func main() {
-	port := os.Getenv("SERVER_PORT")
-	if port == "" {
-		port = "8080"
+	ctx := context.Background()
+
+	cfg, err := config.Load()
+	if err != nil {
+		log.Fatalf("Failed to load config: %v", err)
 	}
 
+	db, err := database.Open(ctx, cfg.DatabaseURL)
+	if err != nil {
+		log.Fatalf("Failed to connect to database: %v", err)
+	}
+	defer db.Close()
+
 	mux := http.NewServeMux()
-	mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
+
+	// Health check.
+	mux.HandleFunc("GET /health", func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
-		fmt.Fprintln(w, "ok")
+		w.Write([]byte("ok"))
 	})
 
-	log.Printf("MrixsCraft Server starting on :%s", port)
-	if err := http.ListenAndServe(":"+port, mux); err != nil {
-		log.Fatal(err)
+	// Yggdrasil API.
+	authHandler := auth.NewHandler(db, cfg)
+	authHandler.RegisterRoutes(mux)
+
+	// TODO: register API, Admin, CAS routes.
+
+	addr := ":" + itoa(cfg.Port)
+	srv := &http.Server{
+		Addr:    addr,
+		Handler: mux,
 	}
+
+	// Graceful shutdown.
+	done := make(chan os.Signal, 1)
+	signal.Notify(done, syscall.SIGINT, syscall.SIGTERM)
+
+	go func() {
+		log.Printf("MrixsCraft Server starting on %s", addr)
+		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("Server error: %v", err)
+		}
+	}()
+
+	<-done
+	log.Println("Shutting down…")
+
+	shutdownCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	if err := srv.Shutdown(shutdownCtx); err != nil {
+		log.Printf("Shutdown error: %v", err)
+	}
+	log.Println("Stopped.")
+}
+
+// itoa converts int to string (stdlib alias to avoid fmt import just for this).
+func itoa(n int) string {
+	return strconv.Itoa(n)
 }