Close two milestone-fieldtest doc-gaps (F6/F8) with one pass now that the
surfaces are stable. A newcomer could only learn the three headless JSON
artifact kinds from the fieldtest corpus: the op-script grammar was
undocumented (#208) and there was no worked process/campaign example nor a
pointer to the discoverable metric vocabulary (#197).
Add docs/authoring-guide.md — a worked, verified example per artifact kind
(op-script -> graph build; process document -> process validate/register;
campaign document -> campaign validate/register/run), every command run
against the binary and its output transcribed. Documents all six ops
(source/input/add/feed/connect/expose) with their JSON shapes, and teaches
the metric roster split (rankable / gate / | generalize) pointing at
'aura process introspect --metrics' as the source of truth rather than
hand-copying the rosters. A short paragraph in project-layout.md links it.
Docs only; no code or CLI change (the surfaces already suffice). Grammar
grounded on construction.rs; examples faithful to the milestone corpus.
closes#197closes#208
Brummel
e7c7bded3e