docs(skill): add verified anti-pattern deltas to the formula and data authoring skills
Documentation-only. Both skills were already mature, so this adds only the verified gaps from this season (no padding):
- objectstack-formula: only the stdlib + CEL built-ins are callable — an UNKNOWN
function now FAILS
objectstack build(#1877), not a silent runtime no-op. - objectstack-data: a
multiple: truelookup is an ARRAY column (not a junction object) — reference positionally (#1872); and on insert an omitted optional field reads asnullin validation predicates (#1871).