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/profile/history/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
     import { fileUrl } from '$lib/api/client';
+    import { chapterLabel } from '$lib/api/chapters';
     import { clearReadProgress, type ReadProgressSummary } from '$lib/api/read_progress';
     import BookImage from '@lucide/svelte/icons/book-image';
     import Trash2 from '@lucide/svelte/icons/trash-2';
@@ -186,7 +187,7 @@
                                 <a href="/manga/{u.manga_id}" class="title">{u.manga_title}</a>
                                 <span class="target">
                                     <a href="/manga/{u.manga_id}/chapter/{u.chapter.id}">
-                                        Chapter {u.chapter.number}{#if u.chapter.title}: {u.chapter.title}{/if}
+                                        {chapterLabel(u.chapter)}
                                     </a>
                                     <span class="muted">({u.chapter.page_count} pages)</span>
                                 </span>