fix: reader loads the full chapter list for prev/next and the dropdown

The reader fetched only the first 200 chapters, so a deep chapter (#250) fell
outside the window and its prev/next chevrons resolved to null — a dead end —
and the chapter dropdown was truncated. Add listAllChapters, which pages
through the API's 200-row cap, and use it in the reader loader.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/api/chapters.ts

@@ -40,6 +40,28 @@ export async function listChapters(
     );
 }
 
+/**
+ * Every chapter of a manga, in display order, paging through the API (which
+ * clamps `limit` to 200 per request). The reader needs the complete list so
+ * prev/next navigation and the chapter dropdown work for a deep chapter — a
+ * single 200-row window dead-ended chapter #250 with null neighbours.
+ */
+export async function listAllChapters(mangaId: string): Promise<Chapter[]> {
+    const PAGE = 200;
+    const all: Chapter[] = [];
+    let offset = 0;
+    // Hard iteration cap (200 * 100 = 20k chapters) so a bad `total` can never
+    // spin forever.
+    for (let i = 0; i < 100; i++) {
+        const { items, page } = await listChapters(mangaId, { limit: PAGE, offset });
+        all.push(...items);
+        offset += items.length;
+        const total = page.total ?? all.length;
+        if (items.length < PAGE || all.length >= total) break;
+    }
+    return all;
+}
+
 export async function getChapter(mangaId: string, chapterId: string): Promise<Chapter> {
     return request<Chapter>(
         `/v1/mangas/${encodeURIComponent(mangaId)}/chapters/${encodeURIComponent(chapterId)}`