feat: improve CLI help layout with command groups and cleaner format #90

Description:

Describe the Feature

Currently, when running becwright without arguments or running becwright --help, it outputs Python's default, dense argparse printout. This list all 15+ subcommands in a single line:

usage: becwright [-h] [--version] {check,init,why,run,check-msg,validate,doctor,demo,list,mcp,install,uninstall,export,import,add,search} ...
becwright: error: the following arguments are required: command

This is hard to scan and read, especially for new developers trying to understand what subcommands are available.

We should improve the CLI output by grouping commands logically (similar to docker, git, or pip) and introducing clean alignment, colorization (optional/using existing style helpers), and explicit command category groupings.

Implementation Plan

1. Override the default help formatter in cli.py or intercept empty args/--help in main().
2. Format output programmatically with clean indentation and headers.
3. Keep the individual subcommand helpers (becwright check --help) intact via the standard subparser help formatters.