fix: page through all chapters when the API omits total

listAllChapters used `page.total ?? all.length` as the loop bound. The
/chapters endpoint always returns `total: null`, so a full 200-row first
page broke the loop immediately — the reader dead-ended past chapter 200.
Stop on a short page instead; only trust `total` when actually reported.

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

frontend/src/lib/api/chapters.ts

@@ -56,8 +56,11 @@ export async function listAllChapters(mangaId: string): Promise<Chapter[]> {
         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;
+        // A short page is the only reliable end-of-list signal: the /chapters
+        // endpoint returns `total: null`, so we can't infer completion from it.
+        // Only stop early on `total` when the API actually reports one.
+        if (items.length < PAGE) break;
+        if (page.total != null && all.length >= page.total) break;
     }
     return all;
 }