cli: pass -h/--help to subcommands instead of intercepting in main parser #191

Problem

The qcom-ptool CLI dispatcher intercepts -h and --help flags even when a subcommand is specified (e.g. qcom-ptool gen_partition -h or qcom-ptool gen_udev_rules -h), printing the top-level CLI help instead of delegating to the subcommand's help handler.

This contradicts the top-level help message epilog and README which state:
Run 'qcom-ptool <subcommand> -h' to see the options accepted by each subcommand.

Additionally, show.py fails with getopt.GetoptError: option -h not recognized because -h/--help is not handled in its options list.

Current Behavior

Running qcom-ptool <subcommand> -h or qcom-ptool <subcommand> --help prints the top-level qcom-ptool help:

usage: qcom-ptool [-h] [-V] subcommand

Qualcomm partition tool - GPT partition table generator and mass storage
programmer.
...
Run 'qcom-ptool <subcommand> -h' to see the options accepted by each
subcommand.

The subcommand is never invoked and its options/usage cannot be viewed.

Expected Behavior

When a valid subcommand is given, flags such as -h and --help should be passed to that subcommand so the user can inspect the options accepted by each subcommand.

Reproduction

Run:
qcom-ptool gen_udev_rules -h or qcom-ptool gen_partition -h
Observe that the top-level qcom-ptool help is displayed instead of the subcommand usage.

Technical Context

In qcom_ptool/cli.py, _build_parser() creates an argparse.ArgumentParser with default add_help=True. When parser.parse_known_args() runs on ["gen_udev_rules", "-h"], argparse intercepts -h, prints the top-level help, and terminates immediately before runpy.run_module can be called.
In qcom_ptool/show.py, getopt.getopt() only accepts ["board=", "hlos=", "boot-fw=", "root="] and does not accept -h / --help.