feat: Implement CLI framework with Cobra

- Add root command with Cobra framework
- Implement shell completion support for bash/zsh/fish/powershell
- Add version command
- Add configuration initialization on startup via PersistentPreRunE
- Include verbose (-v/-vv) and debug flags
- Set up proper error handling and exit codes

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

cmd/hostkeeper/root.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+
+	"git.tukangketik.id/swanadiva/hostkeeper/pkg/config"
+)
+
+var (
+	cfgFile string
+	appCfg  *config.Config
+	verbose int
+	debug   bool
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "hostkeeper",
+	Short: "Cross-platform SSH/SFTP management tool",
+	Long: `Hostkeeper - Cross-platform SSH/SFTP Management Tool
+
+A comprehensive SSH/SFTP management tool with secure credential storage,
+host management, and cross-device sync capabilities.
+
+Quick Start:
+  hostkeeper add myserver --host 192.168.1.10 --user admin
+  hostkeeper list
+  hostkeeper connect myserver
+
+For more information, visit the project repository.`,
+	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
+		// Initialize configuration
+		cfg, err := config.New()
+		if err != nil {
+			return fmt.Errorf("failed to initialize config: %w", err)
+		}
+		appCfg = cfg
+		return nil
+	},
+}
+
+func init() {
+	cobra.OnInitialize(initConfig)
+
+	rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is platform-specific app dir)")
+	rootCmd.PersistentFlags().CountVarP(&verbose, "verbose", "v", "verbose output (-v for info, -vv for debug)")
+	rootCmd.PersistentFlags().BoolVar(&debug, "debug", false, "enable debug mode")
+
+	rootCmd.AddCommand(versionCmd)
+}
+
+// initConfig reads in config file and ENV variables if set
+func initConfig() {
+	if cfgFile != "" {
+		viper.SetConfigFile(cfgFile)
+	} else {
+		// Use platform-specific config directory
+		cfg, err := config.New()
+		if err != nil {
+			return
+		}
+		viper.AddConfigPath(cfg.GetConfigDir())
+		viper.SetConfigType("json")
+		viper.SetConfigName("config")
+	}
+
+	viper.AutomaticEnv()
+
+	// Read config file (ignore if not found for first run)
+	_ = viper.ReadInConfig()
+}
+
+var versionCmd = &cobra.Command{
+	Use:   "version",
+	Short: "Print the version number",
+	Long:  `Print the version and build information for HostKeeper.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Printf("hostkeeper %s (built: %s)\n", version, buildTime)
+	},
+}
+
+// Execute runs the root command
+func Execute() error {
+	return rootCmd.Execute()
+}