feat(cli): campaign validate runs the executor preflight as a third tier (fieldtest 0108 F6)

valid == runnable for every pure document/campaign property: inside a
project, once intrinsic + referential pass, validate fetches the
referenced process from the store and runs the data-free
aura_campaign::preflight (promoted to pub) — an executable shape gains
'campaign document valid (executable): pipeline shape and static
guards pass'; a shape/param/metric/instrument fault refuses under
'campaign is not executable:' with the exec_fault_prose detail, exit 1,
before any member runs. Outside a project the skip line is unchanged
(the third tier needs the store like the second).

Collateral the RED author predicted: the referential e2e's OK fixture
(PROCESS_DOC: deflate+plateau sweep, overfit_probability gate) was
intrinsically-valid-but-never-executable — that test now registers an
executable twin (argmax/no-deflate, per-member gate metric); the base
PROCESS_DOC fixture stays untouched for all other consumers.

RED-first (tdd-author handoff): the third-tier pin observed failing on
the two-line validate output.

Gates: workspace 1026/0, clippy -D warnings clean.

closes #205

crates/aura-campaign/src/lib.rs

@@ -177,7 +177,7 @@ fn predicate_holds(cmp: &Cmp, value: f64, threshold: f64) -> bool {
 /// needs >= 2 campaign instruments and an R selection metric (the registry's
 /// `check_r_metric`). The campaign parameter carries the campaign-level
 /// static checks (generalize's instrument arity).
-pub(crate) fn preflight(process: &ProcessDoc, campaign: &CampaignDoc) -> Result<(), ExecFault> {
+pub fn preflight(process: &ProcessDoc, campaign: &CampaignDoc) -> Result<(), ExecFault> {
     // Position of a stage in the fixed v2 shape; gates (rank 1) may repeat,
     // every other rank appears at most once and ranks never decrease.
     fn shape_rank(stage: &StageBlock) -> usize {