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/lib/plexStats.test.ts

@@ -1,4 +1,7 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
+
+// format.ts boots i18n on import (localStorage); the formatters here take the language as an argument.
+vi.mock("../i18n", () => ({ default: { t: (k: string) => k } }));
 import {
   buildStatRows,
   createFragMeter,
@@ -17,25 +20,28 @@ const DASH = "—";
 
 describe("plexStats formatters", () => {
   it("fmtBitrate scales kbps/Mbps and dashes zero/undefined", () => {
-    expect(fmtBitrate(undefined)).toBe(DASH);
-    expect(fmtBitrate(0)).toBe(DASH);
-    expect(fmtBitrate(820_000)).toBe("820 kbps");
-    expect(fmtBitrate(4_200_000)).toBe("4.2 Mbps");
-    expect(fmtBitrate(1_000_000)).toBe("1.0 Mbps");
+    expect(fmtBitrate(undefined, "en")).toBe(DASH);
+    expect(fmtBitrate(0, "en")).toBe(DASH);
+    expect(fmtBitrate(820_000, "en")).toBe("820 kbps");
+    expect(fmtBitrate(4_200_000, "en")).toBe("4.2 Mbps");
+    expect(fmtBitrate(1_000_000, "en")).toBe("1.0 Mbps");
+    expect(fmtBitrate(4_200_000, "hu")).toBe("4,2 Mbps"); // E30 S3: the UI language's decimal mark
   });
 
   it("fmtBufferSecs shows one decimal, dashes negatives/non-finite", () => {
-    expect(fmtBufferSecs(12.34)).toBe("12.3 s");
-    expect(fmtBufferSecs(0)).toBe("0.0 s");
-    expect(fmtBufferSecs(-1)).toBe(DASH);
-    expect(fmtBufferSecs(Infinity)).toBe(DASH);
+    expect(fmtBufferSecs(12.34, "en")).toBe("12.3 sec");
+    expect(fmtBufferSecs(0, "en")).toBe("0.0 sec");
+    expect(fmtBufferSecs(12.34, "hu")).toBe("12,3 mp");
+    expect(fmtBufferSecs(-1, "en")).toBe(DASH);
+    expect(fmtBufferSecs(Infinity, "en")).toBe(DASH);
   });
 
   it("fmtFrames shows ratio + drop %, dashes when nothing decoded", () => {
-    expect(fmtFrames(0, 0)).toBe(DASH);
-    expect(fmtFrames(0, 1000)).toBe("0 / 1000 (0.00%)");
-    expect(fmtFrames(5, 1000)).toBe("5 / 1000 (0.50%)");
-    expect(fmtFrames(30, 1000)).toBe("30 / 1000 (3.0%)");
+    expect(fmtFrames(0, 0, "en")).toBe(DASH);
+    expect(fmtFrames(0, 1000, "en")).toBe("0 / 1,000 (0.00%)");
+    expect(fmtFrames(5, 1000, "en")).toBe("5 / 1,000 (0.50%)");
+    expect(fmtFrames(30, 1000, "en")).toBe("30 / 1,000 (3.0%)");
+    expect(fmtFrames(30, 1000, "hu")).toBe("30 / 1000 (3,0%)");
   });
 
   it("fmtRes dashes an undecoded 0×0 frame", () => {
@@ -68,6 +74,7 @@ describe("plexStats formatters", () => {
 
 describe("buildStatRows", () => {
   const base: PlexStatsInput = {
+    lang: "en",
     playable: "remux",
     transport: "hls",
     videoWidth: 1280,
@@ -199,6 +206,7 @@ describe("measured bitrate", () => {
 
 describe("buildStatRows — what is actually playing", () => {
   const hls = (over: Partial<PlexStatsInput> = {}): PlexStatsInput => ({
+    lang: "en",
     playable: "remux",
     transport: "hls",
     videoWidth: 1920,