profile-config gains two optional keys for the country-poster-wall profile: `countries` (ISO-3 codes, or
{code, name, count} records, in the host's order) and `region` (one WAGF region as the data names it).
With either, the wall is flat: one section, nothing collapsed, two columns unless `columns` says otherwise,
no heading unless `heading` is given, because it sits under the host's own region heading. A requested
country with no poster keeps its card and says so in the regions catalogue's words. With neither key,
every binding is what it was, so the plain wall is unchanged. PosterWall itself is untouched; only the
country-posters bundle rebuilds. The usage lines in index.js and the profile's meta note name the keys.
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