fix(chapters): sort chapter list entries, localize strings, fix tick keys

utils/chapters.test.ts

@@ -3,6 +3,7 @@ import {
   chapterMarkers,
   currentChapterIndex,
   formatChapterTime,
+  sortedChapters,
 } from "./chapters";
 
 // Helper: a ChapterInfo with a start in milliseconds.
@@ -48,6 +49,23 @@ describe("currentChapterIndex", () => {
   });
 });
 
+describe("sortedChapters", () => {
+  test("pairs each chapter with its ms start, sorted ascending", () => {
+    const a = ch(60_000, "C");
+    const b = ch(0, "A");
+    const c = ch(30_000, "B");
+    expect(sortedChapters([a, b, c])).toEqual([
+      { chapter: b, positionMs: 0 },
+      { chapter: c, positionMs: 30_000 },
+      { chapter: a, positionMs: 60_000 },
+    ]);
+  });
+  test("returns [] for null/undefined", () => {
+    expect(sortedChapters(null)).toEqual([]);
+    expect(sortedChapters(undefined)).toEqual([]);
+  });
+});
+
 describe("formatChapterTime", () => {
   test("formats m:ss and h:mm:ss", () => {
     expect(formatChapterTime(65_000)).toBe("1:05");