`gbrain bootstrap <subcommand> --help` (a help token AFTER the subcommand
name, e.g. `gbrain bootstrap uninstall --help`) fell through into the
subcommand's own arg parsing instead of printing help, since none of the
mutating handlers (repo/hooks/verify/attach/uninstall/render/interview)
checked for --help/-h/help themselves. `uninstall --help` ran a real
uninstall; `repo --help` created a real private GitHub repo; etc.
Add a SUBCOMMAND_HELP usage map plus a pre-dispatch hasHelpToken() guard in
runBootstrap so a help token anywhere in the subcommand's args short-circuits
before any lock/runner/engine/handler call. Bare `help` (no dashes) is also
recognized, except for `interview` (its --set KEY value free-text answers
could legitimately be the literal word "help").
New test/bootstrap-subcommand-help.serial.test.ts arms fixtures so the real
operation would reach its side effect if the guard were removed (an
already-rendered workspace for render/hooks/attach, an operational verify
config, an isolated uninstall home with a real receipt-tracked file, a fresh
interview workspace) and asserts nothing mutates.
