refactor(i18n): ask the catalogue for a sentence in one helper

`t()` answers a missing key with the key, so "does this code have a
sentence" was a comparison written inline at every site that wanted a
code's sentence or a fallback, twenty-odd times in several spellings.
translateOrNull, translateCodeOrNull and translateCode in
src/lib/i18n/translate-code.ts now hold that probe, every site uses
them, and a guard refuses the inline comparison anywhere else.

src/components/links/related-records.tsx

@@ -63,6 +63,7 @@ import type { EncounterDTO } from "@/lib/encounters/dto";
 import type { IllnessEpisodeDTO } from "@/lib/illness/dto";
 import type { RelatedLink } from "@/lib/links/related";
 import type { EncounterKind } from "@/generated/prisma/client";
+import { translateOrNull } from "@/lib/i18n/translate-code";
 
 type Translate = ReturnType<typeof useTranslations>["t"];
 type RelatedKind = RelatedLink["kind"];
@@ -114,9 +115,8 @@ function rowLabel(t: Translate, row: RelatedLink): string {
   // A dose without a written name arrives as its catalogue slug ("tetanus"),
   // named here from the reader's bundle the way the dose picker names it.
   if (row.kind === "vaccination" && /^[a-z0-9_-]+$/.test(row.label)) {
-    const key = `vaccinations.catalog.${row.label}`;
-    const name = t(key);
-    if (name !== key) return name;
+    const name = translateOrNull(t, `vaccinations.catalog.${row.label}`);
+    if (name !== null) return name;
   }
   return row.label;
 }