Correct the surviving Luma and content-layout prose that contradicts the moved pins

_docs/runbooks/data-ingest.md §8 lines 1023-1029 still lead with:

The default --luma-source no longer validates.

and send the reader to .local/migration-data/events/luma-aggregate-v1.backup-20260902
as the directory that works.

Both halves are now false, and in the most damaging direction: f100d16d
(2026-09-06) re-pinned _docs/migration-data/event-registration-sources.json
to event_total: 174 with the 174-directory's tree_sha256. Verified during
#321: recomputing the protected-tree digest of
.local/migration-data/events/luma-aggregate-v1 with the repository's own
algorithm reproduces the pinned 2e18d184...52e3c2 exactly over 174 CSV/JSON
pairs, and derive_registration_sources(...) against the default
--luma-source returns luma {events: 174, rows: 52467, eligible: 52415, excluded: 52} with both the checksum gate (scripts/prod/import_events.py:786)
and the facts gate (:806) passing.

So the default path validates, and the 166-event backup-20260902 directory the
prose recommends is now the one that would fail the pin. This is the last
place in the repository that can still send an operator at the wrong export
directory, which is why it is filed ahead of the other surviving echoes.

#321 closed the §12 entry (old item 10) and recorded the closure in §12.1, but
its grooming put §8 prose out of scope, so the contradiction now sits inside one
document.

Scope: correct the §8 blockquote to match the moved pin and point it at the
§12.1 row. _docs/runbooks/data-ingest.md §6.1 lines 515-521 carry the same
class of survival — a season-hierarchy paragraph superseded by the closure of
old item 15 — and belongs in the same change: both are §6/§8 echoes of §12
entries that closed.

Explicit non-goal: re-opening the pin decision. It was made on 2026-09-06.

Refs #310

Read _docs/runbooks/data-ingest.md §8 lines 1023-1029 and §6.1 lines 515-521, then compare both passages with the closed entries and closure recorded in §12.1. Update the stale export-path and season-hierarchy prose without revisiting the pin decision; done means neither section contradicts the moved pin or the closed §12 items.