Implement web API foundation

Add application container, Gin router, graceful shutdown handler,
and version endpoint. This establishes the skeleton for the WebDisk
HTTP API as described in the architecture.

- Add internal/app/WebApp for runtime dependencies and version
- Add internal/server/router with GET /api/v1/version route
- Add graceful shutdown runner with signal handling in cmd/serve
- Add internal/api/ErrorResponse for standard HTTP error body
- Update roadmap, architecture, and decisions documentation

cmd/serve.go

@@ -0,0 +1,43 @@
+package cmd
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/spf13/cobra"
+
+	"github.com/dhao2001/mygo/internal/app"
+	"github.com/dhao2001/mygo/internal/config"
+	"github.com/dhao2001/mygo/internal/server"
+)
+
+var serveConfigFile string
+
+var serveCmd = &cobra.Command{
+	Use:   "serve",
+	Short: "Start the MyGO HTTP server",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		v := config.New()
+		cfg, err := config.Load(v, serveConfigFile)
+		if err != nil {
+			return fmt.Errorf("load config: %w", err)
+		}
+
+		ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+		defer stop()
+
+		webApp := app.NewWebApp(cfg)
+		router := server.NewRouter(webApp)
+		addr := server.Address(webApp.Config.Server)
+
+		return server.RunWithGracefulShutdown(ctx, addr, router)
+	},
+}
+
+func init() {
+	serveCmd.Flags().StringVar(&serveConfigFile, "config", "", "config file path")
+	rootCmd.AddCommand(serveCmd)
+}