fix(i18n): numbers, units, dates and order in the UI language, and after a switch (E30 S3)

Every locale formatter takes the language as an argument. Under the React
Compiler a formatter that read the i18n singleton was memoized on its other
arguments, so a card kept "2 hr 4 min" after a switch to Hungarian; plexLang()
had the same flaw and left Plex queries in the old language. Components now
take the language from useTranslation, and the signature makes forgetting it
a type error.

- ratings, file sizes, stream stats: the language's decimal mark ("8,3")
- view and subscriber counts compact in the language ("1,2 E")
- seconds as the language's unit ("6 mp") in the sliders and the stats
- a person's birth and death dates as dates, not ISO strings
- A-Z lists by the shown name in the language's alphabet (compareText),
  the tag catalog re-sorted by its translated names
- lint local/locale-format (was date-format) also refuses Intl.NumberFormat
  outside lib/format.ts, localeCompare, and a component reading the language
  off the i18n singleton

frontend/src/i18n/index.ts

@@ -67,11 +67,13 @@ export function setLanguage(code: LangCode): void {
   document.documentElement.lang = code;
 }
 
-// The Plex overlay serves only EN or HU metadata (E5 S6). Collapse the active UI language to one of
-// those for the `?lang=` param / query keys. Components read `i18n.language` off useTranslation (which
-// re-renders on switch); this singleton reader is for non-component code (e.g. plexPlayerHooks).
-export function plexLang(): "en" | "hu" {
-  return i18n.language?.startsWith("hu") ? "hu" : "en";
+// The Plex overlay serves only EN or HU metadata (E5 S6). Collapse a UI language to one of those for
+// the `?lang=` param / query keys. It takes the language instead of reading the singleton (E30 S3):
+// under the React Compiler a component's `plexLang()` was a value with no reactive input, so it kept
+// the language the component first rendered in — a switch left every Plex query on the old language.
+// A component passes `i18n.language` from useTranslation; non-component code the singleton's.
+export function plexLang(lang: string | undefined): "en" | "hu" {
+  return lang?.startsWith("hu") ? "hu" : "en";
 }
 
 export default i18n;