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/routes/manga/[id]/chapter/[chapter_id]/+page.ts

@@ -1,5 +1,5 @@
 import { getManga } from '$lib/api/mangas';
-import { getChapter, getChapterPages, listChapters } from '$lib/api/chapters';
+import { getChapter, getChapterPages, listAllChapters } from '$lib/api/chapters';
 import { getMyReadProgressForManga } from '$lib/api/read_progress';
 import type { PageLoad } from './$types';
 
@@ -13,19 +13,18 @@ export const load: PageLoad = async ({ params, url }) => {
         // `null` for guests or first-time openers — the reader uses
         // this to seed its session-local high-water mark.
         getMyReadProgressForManga(params.id),
-        // Loaded so the reader can compute prev/next chapter for the
-        // chevron-driven chapter navigation. limit=200 covers every
-        // realistic series; mangas with more chapters will lose some
-        // chapter-jump precision at the tail edge but the in-page
-        // navigation still works fine.
-        listChapters(params.id, { limit: 200 })
+        // The FULL chapter list (paged through the API's 200-row cap) so the
+        // prev/next chevrons and the chapter dropdown work even for a deep
+        // chapter — a single 200-row window dead-ended chapter #250 with null
+        // neighbours.
+        listAllChapters(params.id)
     ]);
     return {
         manga,
         chapter,
         pages,
         readProgress,
-        chapters: chapterList.items,
+        chapters: chapterList,
         // `?page=N` lets the prev-chapter chevron land directly on the
         // last page of the chapter it just navigated to. `last` is a
         // convenience sentinel for "however many pages this chapter