feat(base-commandline): commands, categories, multi-prefix options, and positional argument builder

[deer]

Extends CommandLineParser and the Command fluent builder with four additions that close the remaining gap between base-commandline and a full flat-CLI framework:

• Declarative commands and categories — registerCommand / registerCategory (and Command.command / Command.category) add Commands: and Categories: sections to help output, sorted alphabetically. Section headings are overridable via
  setCommandsSectionName / setCategoriesSectionName (e.g. spin can render Tasks: / Aliases:).
• Multi-prefix options without annotations — CommandLineParser.add(List<String>, Class, methodName, description, paramTypes...) and the matching Command.option(List<String>, ...) overload register an option under multiple prefixes with an
  explicit description, no @CommandLine.Prefix or @CommandLine.Description required.
• Command.positionalArgument(Consumer<String>) — fluent wrapper for setPositionalArgumentConsumer, completing the builder API.
• Help rendering fix — prefixes are now tracked in methodPrefixes at registration time, so explicitly-registered options appear correctly in help (previously only annotation-driven options rendered their prefixes).