i18n: BCP-47 URL locales + complete EN translations

- URL surface now matches Angular: `/ru-ru/`, `/en-us/`, `/zh-cn/`, …
  (BCP-47). Bare short codes still work — the [lang]/layout auto-
  promotes them with a replace navigation. Internally everything that
  needs the short language (i18n file lookup, API path segment,
  Accept-Language header, dictionary `title[lang]` key, Intl
  formatters) reads it through the new `useLocale()` hook, which
  returns both `locale` (BCP-47) and `language` (short).
- ApiClient.locale is now mutable and is updated from the [lang]
  layout whenever the URL locale changes — was hard-coded to "ru" in
  the root layout before, so backend responses for /en/... still came
  back in Russian. Cities / airports / flight statuses now arrive in
  the active language.
- All 21 empty EN translation keys filled in (AIRPLANE.*, BOARD.
  PREVIOUS-FLIGHT, SCHEDULE.FILE-NAME, SEO.SCHEDULE.*, SEO.FLIGHTS-
  MAP.*, SHARED.FLIGHT-TRANSFER-PLURAL-*, SHARED.WEEK_FORMAT-WRONG)
  so /en-us renders without falling back to raw keys.
- Added BOARD.LOAD-FAILED-TITLE / -MESSAGE keys (RU + EN) and removed
  the three hardcoded Russian error strings from the search-page
  error card.
- FlightStatus now reads `FLIGHT-STATUSES.{Status}` from i18n instead
  of hardcoding the Russian labels.
- FlightCard's OperatorLogo now picks the en/ru carrier-logo variant
  from `useLocale().language` instead of always passing "ru" — the
  Aeroflot/Rossiya logos display in the active language where
  variants exist.
- registerPrimeLocales(): all 9 supported languages get a PrimeReact
  `addLocale` entry at module load (RU + EN hand-curated, others built
  from Intl). Calendar/AutoComplete widgets switch with the URL.
- ErrorBoundary catches outside the i18n provider, so it now ships
  its own minimal localised string table keyed off the URL locale —
  no more "Something went wrong" leaking on the Russian site.
- Hreflang URLs now emit BCP-47 (`/en-us/...`) while `hreflang="en"`
  stays the short Google-friendly form.
- Datetime helpers accept either short or BCP-47 locale (`isRussianLocale`)
  so callers can pass through whatever the route hands them.

src/shared/utils/datetime/index.ts

@@ -5,29 +5,38 @@
  * No Angular dependencies, no side effects.
  */
 
+/** Match `ru`, `ru-RU`, `ru-ru`, `RU` — anything starting with `ru` */
+function isRussianLocale(locale: string): boolean {
+  return locale.toLowerCase().startsWith("ru");
+}
+
 /**
  * Format a duration given in total minutes into a human-readable string.
  * Russian units mirror Angular's DurationPipe (SHORT-DAY='д.', SHORT-HOUR='ч.',
  * SHORT-MIN='мин.') so values read as '1ч. 30мин.' not '1ч 30м'.
  *
+ * Accepts either a short language code (`"ru"`) or a full BCP-47 locale
+ * (`"ru-ru"`).
+ *
  * @example formatDuration(150) => "2h 30m"
  * @example formatDuration(150, "ru") => "2ч. 30мин."
+ * @example formatDuration(150, "ru-ru") => "2ч. 30мин."
  * @example formatDuration(0) => "0h 0m"
  */
 export function formatDuration(
   minutes: number,
   locale: string = "en",
 ): string {
-  if (minutes < 0) return locale === "ru" ? "Неизвестно" : "Unknown";
+  const ru = isRussianLocale(locale);
+  if (minutes < 0) return ru ? "Неизвестно" : "Unknown";
 
   const days = Math.floor(minutes / (60 * 24));
   const hours = Math.floor((minutes % (60 * 24)) / 60);
   const mins = Math.floor(minutes % 60);
 
-  const units =
-    locale === "ru"
-      ? { d: "д.", h: "ч.", m: "мин." }
-      : { d: "d", h: "h", m: "m" };
+  const units = ru
+    ? { d: "д.", h: "ч.", m: "мин." }
+    : { d: "d", h: "h", m: "m" };
 
   const daysPart = days > 0 ? `${days}${units.d} ` : "";
   return `${daysPart}${hours}${units.h} ${mins}${units.m}`;
@@ -61,7 +70,7 @@ export function formatDate(
   const d = typeof date === "string" ? new Date(date) : date;
   if (Number.isNaN(d.getTime())) return "";
 
-  return d.toLocaleDateString(locale === "ru" ? "ru-RU" : "en-US", {
+  return d.toLocaleDateString(isRussianLocale(locale) ? "ru-RU" : "en-US", {
     year: "numeric",
     month: "long",
     day: "numeric",