Reject single bare word as implicit note shorthand

Single unrecognized words now print an error with usage hint instead of
being submitted as a note. Prevents typos from creating junk notes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/cmd/root.go

@@ -38,6 +38,9 @@ var rootCmd = &cobra.Command{
 		if len(args) == 0 {
 			return cmd.Help()
 		}
+		if len(args) == 1 {
+			return fmt.Errorf("unknown command %q\nTo add a note, use: kb \"%s ...\" or pass multiple words", args[0], args[0])
+		}
 		note := strings.Join(args, " ")
 		tags, _ := cmd.Flags().GetString("tags")
 		client := api.NewClient()
@@ -48,8 +51,8 @@ var rootCmd = &cobra.Command{
 func init() {
 	api.SetVersionInfo(Version, MinEngineVersion)
 	rootCmd.Version = Version
-	rootCmd.SetUsageTemplate(`Quick note taking:
-  kb "note text" [flags]
+	rootCmd.SetUsageTemplate(`Quick note taking (must be more than one word):
+  kb "note text here" [flags]
 
 Normal usage:
   kb [command] [flags]{{if .HasAvailableSubCommands}}