Optimize eager loading in list endpoint — avoid over-fetching relations

[zigzagdev]

Goal

The current getAllHeritages query eager-loads three relations (countries, images, descriptions) for every item in the paginated list. For a 20-item page this means 3 extra queries minimum, and the data returned is often more than what the list view renders.

What to Do

1. Audit what fields the list response actually exposes (WorldHeritageDtoCollectionFactory → toSummaryArray).
2. For the images relation: the list only needs thumbnail_url which is already covered by main_image_url. If main_image_url is non-null for most records, skip eager-loading images on the list endpoint entirely (or load only when main_image_url IS NULL).
3. For descriptions: the list uses short_description_ja. Evaluate whether this is shown in the list card. If not, remove it from the list query.
4. For countries: only name_en, name_jp, state_party_code are needed — confirm the select is already minimal and tighten if not.
5. Add ->withCount(...) only if aggregate counts are needed; avoid with() for unused relations.

Acceptance Criteria

• Number of DB queries per list page request reduced (measure with Laravel Debugbar or query log)
• List endpoint returns the same payload shape with no missing fields
• Tests pass

Parent Issue

Related: #457