Add --quiet flag, --json output, and config permission check

- Add global --quiet/-q flag to suppress non-error output
- Add --json flag to verify, snapshot rm, and prune commands
- Add config file permission check (warns if world/group readable)
- Update TODO.md to remove completed items

internal/cli/root.go

@@ -13,6 +13,7 @@ type RootFlags struct {
 	ConfigPath string
 	Verbose    bool
 	Debug      bool
+	Quiet      bool
 }
 
 var rootFlags RootFlags
@@ -34,6 +35,7 @@ on the source system.`,
 	cmd.PersistentFlags().StringVar(&rootFlags.ConfigPath, "config", "", "Path to config file (default: $VAULTIK_CONFIG or /etc/vaultik/config.yml)")
 	cmd.PersistentFlags().BoolVarP(&rootFlags.Verbose, "verbose", "v", false, "Enable verbose output")
 	cmd.PersistentFlags().BoolVar(&rootFlags.Debug, "debug", false, "Enable debug output")
+	cmd.PersistentFlags().BoolVarP(&rootFlags.Quiet, "quiet", "q", false, "Suppress non-error output")
 
 	// Add subcommands
 	cmd.AddCommand(