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/components/PlexPersonView.dom.test.tsx

@@ -25,7 +25,12 @@ beforeAll(() => {
 
 vi.mock("react-i18next", async (importOriginal) => {
   const actual = await importOriginal<typeof import("react-i18next")>();
-  return { ...actual, useTranslation: () => ({ t: (key: string) => key }) };
+  // the real instance: these tests switch the language with setLanguage
+  const real = (await import("i18next")).default;
+  return {
+    ...actual,
+    useTranslation: () => ({ i18n: real, t: (key: string) => key }),
+  };
 });
 
 const plexPerson = vi.fn();
@@ -116,7 +121,8 @@ describe("PlexPersonView", () => {
     // E30: TMDB's English department, named through the vocab (key-echo i18n here).
     expect(screen.getByText("vocab.department.Acting")).toBeTruthy();
     expect(screen.getByText("A celebrated actor.")).toBeTruthy();
-    expect(screen.getByText(/1970-01-01/)).toBeTruthy();
+    // E30 S3: the birth date as a date in the UI language, not the raw ISO string
+    expect(screen.getByText("Jan 1, 1970 · Springfield")).toBeTruthy();
     expect(screen.getByText(/plex\.person\.aka/)).toBeTruthy();
     expect(screen.getByText(/Janie D/)).toBeTruthy();
     // "Known for" rail renders its card.