feat(cli): add cobra-based CLI to run WarpBox server

- Add `cmd/main.go` with a new `warpbox` root command and `run` subcommand
- Support `--addr` flag (default `:8080`) and delegate startup to `server.Run`
- Initialize Go module and dependencies (cobra, gin) via `go.mod`/`go.sum` to enable building the new CLI entrypointfeat(cli): add cobra-based CLI to run WarpBox server

- Add `cmd/main.go` with a new `warpbox` root command and `run` subcommand
- Support `--addr` flag (default `:8080`) and delegate startup to `server.Run`
- Initialize Go module and dependencies (cobra, gin) via `go.mod`/`go.sum` to enable building the new CLI entrypoint

cmd/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+
+	"warpbox/lib/server"
+)
+
+func main() {
+	if err := newRootCommand().Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func newRootCommand() *cobra.Command {
+	rootCmd := &cobra.Command{
+		Use:   "warpbox",
+		Short: "WarpBox command line interface",
+		Long:  "WarpBox provides commands for running and managing the WarpBox service.",
+	}
+
+	var addr string
+	runCmd := &cobra.Command{
+		Use:   "run",
+		Short: "Run the HTTP server",
+		Long:  "Run the WarpBox HTTP server. The root endpoint responds with ok.",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return server.Run(addr)
+		},
+	}
+	runCmd.Flags().StringVar(&addr, "addr", ":8080", "HTTP server address")
+
+	rootCmd.AddCommand(runCmd)
+	return rootCmd
+}