Add `help:OP` operation — per-op spec without dumping the full ops list

[fdaviddpt]

Motivation

Today, to recall a single operation's signature, flags, or payload fields, the only options are:

• ./supertool 'ops' — dumps the entire op list (large, costs context just to check one op)
• grep the ops output for the op name — works, but you only get the one-line summary, not the full payload-field spec / examples

There's no way to ask "show me everything about this one op". Intuitively the first thing you try is ./supertool 'help:<op>' — and that returns:

ERROR: unknown operation: help

So the natural discovery path is a dead end.

Request

Add a help:OP operation that prints only the spec for the named op:

./supertool 'help:gl-issue-create'

Expected output: the op's one-line description, full argument/flag syntax, payload fields (for @file ops — e.g. gl-issue-create requires project, optional milestone_id, labels, assignee_ids, estimate, links), and 1-2 examples.

Why it helps

• Cheap single-op lookup instead of re-reading the whole ops dump (context savings — the whole point of supertool).
• Discoverable: help: is the obvious thing to type, and it currently errors.
• For @file payload ops especially, the required-vs-optional fields aren't visible from the ops one-liner. I learned gl-issue-create needs a project field only by hitting ERROR: payload missing required field: project at runtime — help:gl-issue-create should have told me upfront.

Nice-to-have

• help with no arg → short usage + pointer to ops.
• Fuzzy match: help:gl-issue suggests gl-issue / gl-issue-create.

Filed by Max while creating GitLab issues via gl-issue-create.