🤖 feat: implement Cobra CLI with subcommands

- Add new CLI structure in cmd/cli/
- Implement version, server, and greet commands
- Update build script to compile new CLI binary
- Add Cobra dependency to go.mod
- Update ADR 0015 to reflect implementation status
- Update README and AGENTS.md with CLI usage
- Maintain backward compatibility with existing binaries

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

cmd/cli/main.go

@@ -0,0 +1,77 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	"DanceLessonsCoach/pkg/config"
+	"DanceLessonsCoach/pkg/server"
+	"DanceLessonsCoach/pkg/version"
+	"github.com/rs/zerolog/log"
+
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "dance-lessons-coach",
+	Short: "DanceLessonsCoach - API server and CLI tools",
+	Long: `DanceLessonsCoach provides greeting services and API management.
+
+To begin working with DanceLessonsCoach, run:
+  dance-lessons-coach server --help`,
+	SilenceUsage: true,
+}
+
+var versionCmd = &cobra.Command{
+	Use:   "version",
+	Short: "Print version information",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Println(version.Full())
+	},
+}
+
+var serverCmd = &cobra.Command{
+	Use:   "server",
+	Short: "Start the DanceLessonsCoach server",
+	Run: func(cmd *cobra.Command, args []string) {
+		// Load config and start server
+		cfg, err := config.LoadConfig()
+		if err != nil {
+			log.Fatal().Err(err).Msg("Failed to load configuration")
+		}
+		server := server.NewServer(cfg, context.Background())
+		if err := server.Run(); err != nil {
+			log.Fatal().Err(err).Msg("Server failed")
+		}
+	},
+}
+
+var greetCmd = &cobra.Command{
+	Use:   "greet [name]",
+	Short: "Greet someone by name",
+	Args:  cobra.MaximumNArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		name := ""
+		if len(args) > 0 {
+			name = args[0]
+		}
+		fmt.Printf("Hello %s!\n", name)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(versionCmd)
+	rootCmd.AddCommand(serverCmd)
+	rootCmd.AddCommand(greetCmd)
+
+	// Add flags to server command
+	serverCmd.Flags().String("config", "", "Config file path")
+	serverCmd.Flags().String("env", "", "Environment (dev, staging, prod)")
+	serverCmd.Flags().Bool("debug", false, "Enable debug logging")
+}
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		log.Fatal().Err(err).Msg("CLI execution failed")
+	}
+}