🐛 fix: don't bump freshness timestamps on position-only reorder

[jbourdin]

Summary

Reordering archetypes (drag-and-drop) or deck variants only changes the position field, but it re-stamped the entities' update timestamps as if the content had changed. That polluted several "content was updated" signals:

• the sitemap <lastmod> (via Archetype.updatedAt / Deck.updatedAt),
• the JSON-LD dateModified,
• the user-facing "Updated on …" caption in the archetype catalog,
• the catalog's "sort by updated" order (driven by lastPublishedAt).

Investigation surfaced three stamping paths off the same reorder, not one:

1. Archetype::onPreUpdate — bumped updatedAt and lastPublishedAt (via PublishableTimestampsTrait).
2. Deck::onPreUpdate — bumped the deck's own updatedAt.
3. ArchetypeFreshnessListener — listened on Doctrine postUpdate for Deck and re-stamped the parent archetype's lastPublishedAt on any variant save, reorder included.

Changes

• New StructuralChangeTrait — single source of truth for display-ordering fields (['position']) plus an isStructuralOnlyChange(PreUpdateEventArgs) helper.
• Archetype / Deck — their #[ORM\PreUpdate] hooks early-return when position is the only changed field, leaving every timestamp untouched. A change that also touches a real field still bumps as before.
• ArchetypeFreshnessListener — moved update collection from postUpdate to preUpdate (where the change-set is reliably exposed) and applied the same guard. postPersist (new variant = real activity) and postFlush (bulk writer) are unchanged.
• Docs — updated features.md (F2.27) and models/deck.md to describe the reorder rule.

Test plan

• make test — full suite green (new StructuralChangeTest + extended ArchetypeFreshnessListenerTest)
• In dev: drag-reorder archetypes, confirm updated_at / last_published_at stay put while position moves
• In dev: drag-reorder variants within an archetype, confirm neither the deck's updated_at nor the archetype's last_published_at change
• In dev: edit an archetype's (or variant's) content, confirm the timestamps do advance
• Confirm the catalog "Updated on …" caption and "sort by updated" order are unaffected by a reorder

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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