help: filter by prefix, and surface flags through the CLI #57

gitbay <noun> --help lists subcommands and their one-line summaries but no flags. pass() sets DisableFlagParsing and intercepts --help before the server sees it (cmd/gitbay/main.go:117), so the only flag documentation that exists is the registry's Summary string.

Reaching that is awkward:

• help ignores its arguments and prints all 149 entries (internal/control/control.go:164). help issue dumps the whole registry.
• Output is in registration order, so related commands are not adjacent — build, repo secret, runner, help, dashboard appear in sequence.
• ssh git@gitbay.org help | grep '^issue ' works, but only if you already know to do it.

Consequence: anything driving the CLI without prior knowledge — a new user, a script author, an assistant — either guesses flags or reads 149 lines to find one. Running a command bare prints its usage and exits 2, which is the current escape hatch and is not discoverable either.

Asks, in order of value:

1. help <prefix>... filters to matching commands, so help issue prints the 11 issue commands.
2. gitbay <cmd> --help forwards to the server and prints that command's real usage line instead of cobra's Short.
3. Sort or group the unfiltered listing.

Summary currently carries a description and a usage string joined by ": ". Splitting it into Summary + Usage on Command would let 1 and 2 render cleanly, and would let the JSON envelope expose usage to API consumers.