fix(reader): drop "Chapter N:" prefix from chapter title display (0.51.2)

The chapter list on the manga detail page, the reader's chapter-select
dropdown, the continuous-mode chapter bar, the browser tab title, and
the profile upload-history entries all prepended "Chapter {number}:"
in front of the crawled site title. Source titles already include
"Ch.N" themselves and the manga page renders chapters inside an <ol>,
so the prefix duplicated information the user could already see.

A small chapterLabel(c) helper in $lib/api/chapters returns the site
title as-is, falling back to "Chapter {number}" only when the
crawler captured an empty title (link/option stays non-empty). The
five render sites now call it. The previous-/next-chapter nav
buttons still read "Previous chapter (Ch. N)" / "Next chapter (Ch. N)"
since those are wayfinding labels, not title display.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/manga/[id]/+page.svelte

@@ -10,6 +10,7 @@
         type TagRef
     } from '$lib/api/mangas';
     import { resyncManga } from '$lib/api/admin';
+    import { chapterLabel } from '$lib/api/chapters';
     import { listTags, type Tag } from '$lib/api/tags';
     import { session } from '$lib/session.svelte';
     import Chip from '$lib/components/Chip.svelte';
@@ -45,6 +46,11 @@
         continueChapter?.number ?? readProgress?.chapter_number ?? null
     );
     const continueChapterTitle = $derived(continueChapter?.title ?? null);
+    const continueLabel = $derived(
+        continueChapterNumber != null
+            ? chapterLabel({ number: continueChapterNumber, title: continueChapterTitle })
+            : null
+    );
 
     const authors = $derived<AuthorRef[]>(manga.authors);
     const genres = $derived<GenreRef[]>(manga.genres);
@@ -431,7 +437,7 @@
             >
                 <span class="continue-label">Continue reading</span>
                 <span class="continue-target">
-                    Chapter {continueChapterNumber}{#if continueChapterTitle}: {continueChapterTitle}{/if}
+                    {continueLabel}
                     {#if readProgress && readProgress.page > 1}
                         — page {readProgress.page}
                     {/if}
@@ -445,7 +451,7 @@
                 {#each chapters as c (c.id)}
                     <li>
                         <a href="/manga/{manga.id}/chapter/{c.id}">
-                            Chapter {c.number}{#if c.title}: {c.title}{/if}
+                            {chapterLabel(c)}
                         </a>
                         <span class="pages">({c.page_count} pages)</span>
                     </li>