feat: fix recently-updated section + hideable home sections

Fix "Recently Updated" showing stale books: replace meta_updated
sorting (only changes on metadata writes) with chapters_idx sorted
by -created, so the section now reflects actual chapter activity.

Add per-section show/hide toggles on the home page, persisted in
localStorage via Svelte 5 $state. Each section header gets a small
hide button; hidden sections appear as restore chips above the footer.
Toggleable: Recently Updated, Browse by Genre, From Following.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/lib/server/pocketbase.ts

@@ -299,7 +299,8 @@ export async function invalidateBooksCache(): Promise<void> {
 	await Promise.all([
 		cache.invalidate(BOOKS_CACHE_KEY),
 		cache.invalidate(HOME_STATS_CACHE_KEY),
-		cache.invalidatePattern('books:recent:*')
+		cache.invalidatePattern('books:recent:*'),
+		cache.invalidatePattern('books:recently-updated:*')
 	]);
 }
 
@@ -312,10 +313,46 @@ export async function recentlyAddedBooks(limit = 6): Promise<Book[]> {
 	const cached = await cache.get<Book[]>(key);
 	if (cached) return cached;
 	const books = await listN<Book>('books', limit, '', '-meta_updated');
-	await cache.set(key, books, 5 * 60); // 5 minutes
+	await cache.set(key, books, 5 * 60);
 	return books;
 }
 
+/**
+ * Books with the most recently added chapters, ordered by chapter insertion time.
+ * Queries chapters_idx sorted by -created, deduplicates by slug, then loads books.
+ * This correctly reflects actual chapter activity, unlike meta_updated on books.
+ */
+export async function recentlyUpdatedBooks(limit = 8): Promise<Book[]> {
+	const key = `books:recently-updated:${limit}`;
+	const cached = await cache.get<Book[]>(key);
+	if (cached) return cached;
+
+	// Fetch enough recent chapter rows to find `limit` distinct books
+	const rows = await listN<{ slug: string; created: string }>(
+		'chapters_idx', limit * 25, '', '-created'
+	);
+
+	const seen = new Set<string>();
+	const slugs: string[] = [];
+	for (const row of rows) {
+		if (!seen.has(row.slug)) {
+			seen.add(row.slug);
+			slugs.push(row.slug);
+			if (slugs.length >= limit) break;
+		}
+	}
+
+	if (!slugs.length) return [];
+
+	const books = await getBooksBySlugs(new Set(slugs));
+	// Restore recency order (getBooksBySlugs returns in title sort order)
+	const bookMap = new Map(books.map((b) => [b.slug, b]));
+	const ordered = slugs.flatMap((s) => (bookMap.has(s) ? [bookMap.get(s)!] : []));
+
+	await cache.set(key, ordered, 5 * 60);
+	return ordered;
+}
+
 export interface HomeStats {
 	totalBooks: number;
 	totalChapters: number;