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/lib/api/chapters.ts

@@ -14,6 +14,10 @@ export type ChaptersPage = {
     page: Page;
 };
 
+export function chapterLabel(c: Pick<Chapter, 'number' | 'title'>): string {
+    return c.title ?? `Chapter ${c.number}`;
+}
+
 export type ListOptions = {
     limit?: number;
     offset?: number;