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/ui/ItemCount.dom.test.tsx

@@ -30,7 +30,7 @@ describe("ItemCount", () => {
     render(<ItemCount count={192045} />);
     // Separators come from the shared formatNumber — compare against it, not a fixed en-US string,
     // so the test asserts ItemCount's formatting path rather than the CI locale.
-    expect(text()).toBe(`${formatNumber(192045)} items`);
+    expect(text()).toBe(`${formatNumber(192045, "en")} items`);
   });
 
   // The pill used `count.toLocaleString()`, which groups in the BROWSER's locale: a Hungarian UI on
@@ -52,7 +52,9 @@ describe("ItemCount", () => {
   it("collapses a count of a million or more to 1M+, with the exact figure in the tooltip", () => {
     render(<ItemCount count={1_000_000} />);
     expect(text()).toBe("1M+ items"); // the "1M+" collapse is locale-independent
-    expect(screen.getByTestId("item-count").getAttribute("title")).toBe(formatNumber(1_000_000));
+    expect(screen.getByTestId("item-count").getAttribute("title")).toBe(
+      formatNumber(1_000_000, "en"),
+    );
   });
 
   it("shows the icon-only fixed box (empty label) while the count is undefined", () => {