@lde/search: preserve all label language variants in text projection + resolution

[ddeboer]

Problem

A label-source label text field declares a fixed locale set (locales: [nl, en]), and projection emits only those declared locales. But label data is routinely untagged or tagged in another language:

foaf:name "Bibliothèque"@fr
dct:title "Thésaurus"          # untagged

Every such value is silently dropped, so the facet bucket / reference renders as a bare IRI instead of a label.

The Dataset Register works around this by re-tagging each subject into explicit @nl / @en with a nl → en → first-of-any fallback. That is lossy: it discards the real language, and a subject with both @fr and @de keeps only the first-seen.

Desired behaviour

Preserve every language variant, so [LanguageString!] returns them all, best-first per Accept-Language, and the consumer picks. Once projection keeps all languages, the DR re-tagging workaround disappears.

Two spots hardcode the declared locales and both must change:

1. Projection — applyText (@lde/search) iterates field.locales only.
2. Resolution — the Typesense engine’s localizedValue reads only the field.locales display fields; labelValue additionally falls back to the bare label for untagged (und). So even if the collection stored label_fr, the engine would not read it today.

Two possible shapes

• (a) open / dynamic locale set — project label_<lang> for whatever languages are present and resolve them back into the full LanguageString[]. Keeps per-language search tokenisation (matters for label-collection typeahead, Search-within-a-facet (facet_query typeahead) for high-cardinality facets beyond the maxFacetValues cap #533). (Leaning this way for label collections that are searched, not only displayed.)
• (b) language-map field — store the label as one { lang: value } map and pass it through at resolution. Simplest; loses per-language search tokens, acceptable while a label-source label is display-only.

Decide per use: a display-only reference label can take (b); a searchable label collection needs (a).

Scope

• @lde/search: applyText projects all present languages (not just declared ones) for the chosen shape.
• @lde/search-typesense: localizedValue / labelValue resolve the full variant set back into LanguageString[], best-first per Accept-Language.
• Remove the DR-side re-tagging workaround once projection preserves languages.

Relates

• Sub-issue of Search as a Configurable Pipeline instance: transactional Writer, two update modes, per-reference label sources #534.
• @lde/search: per-reference label sources #537 — per-reference label sources (the label field this extends).
• Search-within-a-facet (facet_query typeahead) for high-cardinality facets beyond the maxFacetValues cap #533 — facet-by-name typeahead (why per-language search tokens matter → shape (a)).
• search: single-type projection + iterable input; search-typesense: return minted collection name #579 — gap 4 of that issue. (Gap 2 shipped in feat(search): accept Iterable<Quad> in projectGraph #580; gaps 1 & 3 → @lde/search-typesense: multi-collection blue/green Writer (route a whole-schema projection to per-type collections) #590.)