feat(reader): chapter comments + readers-this-week count

- CommentsSection now accepts a chapter prop and scopes comments to that chapter
- Chapter reader page mounts CommentsSection with current chapter number
- Book detail page shows rolling 7-day unique reader count badge
- API GET/POST pass chapter param; pocketbase listComments filters by chapter

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

ui/src/lib/server/pocketbase.ts

@@ -1130,6 +1130,7 @@ export async function updateUserAvatarUrl(userId: string, avatarUrl: string): Pr
 export interface PBBookComment {
 	id: string;
 	slug: string;
+	chapter?: number;   // 0 or absent = book-level; N = chapter N
 	user_id: string;
 	username: string;
 	body: string;
@@ -1150,25 +1151,26 @@ export interface CommentVote {
 export type CommentSort = 'top' | 'new';
 
 /**
- * List top-level comments for a book.
+ * List top-level comments for a book or a specific chapter.
+ * chapter=0 (default) → book-level comments only
+ * chapter=N           → comments for chapter N only
  * sort='top'  → by net score (upvotes − downvotes) desc, then newest
  * sort='new'  → newest first (default)
  * Replies (parent_id != "") are NOT included — fetch them separately.
  */
 export async function listComments(
 	slug: string,
-	sort: CommentSort = 'new'
+	sort: CommentSort = 'new',
+	chapter = 0
 ): Promise<PBBookComment[]> {
 	const token = await getToken();
 	const slugEsc = slug.replace(/"/g, '\\"');
-	// Only top-level comments (parent_id is empty or missing)
-	const filter = encodeURIComponent(`slug="${slugEsc}"&&(parent_id=""||parent_id=null)`);
-	// PocketBase sorts: for 'top' we still fetch all and re-sort in JS because
-	// PocketBase doesn't support computed sort fields.  For 'new' we push the
-	// sort down to the DB so large result sets are still paged correctly.
-	const pbSort = sort === 'new' ? '&sort=-created' : '&sort=-created';
+	const chapterFilter = chapter > 0
+		? `&&chapter=${chapter}`
+		: `&&(chapter=0||chapter=null)`;
+	const filter = encodeURIComponent(`slug="${slugEsc}"${chapterFilter}&&(parent_id=""||parent_id=null)`);
 	const res = await fetch(
-		`${PB_URL}/api/collections/book_comments/records?filter=${filter}${pbSort}&perPage=200`,
+		`${PB_URL}/api/collections/book_comments/records?filter=${filter}&sort=-created&perPage=200`,
 		{ headers: { Authorization: `Bearer ${token}` } }
 	);
 	if (!res.ok) return [];
@@ -1179,13 +1181,32 @@ export async function listComments(
 			const scoreB = (b.upvotes ?? 0) - (b.downvotes ?? 0);
 			const scoreA = (a.upvotes ?? 0) - (a.downvotes ?? 0);
 			if (scoreB !== scoreA) return scoreB - scoreA;
-			// tie-break: newest first
 			return new Date(b.created).getTime() - new Date(a.created).getTime();
 		});
 	}
 	return items;
 }
 
+/**
+ * Count unique readers for a book in the last 7 days.
+ * Uses progress.updated timestamp; counts both session-based and user-based.
+ */
+export async function countReadersThisWeek(slug: string): Promise<number> {
+	const token = await getToken();
+	const cutoff = new Date(Date.now() - 7 * 24 * 60 * 60 * 1000).toISOString();
+	const filter = encodeURIComponent(`slug="${slug.replace(/"/g, '\\"')}"&&updated>"${cutoff}"`);
+	const res = await fetch(
+		`${PB_URL}/api/collections/progress/records?filter=${filter}&perPage=500&fields=user_id,session_id`,
+		{ headers: { Authorization: `Bearer ${token}` } }
+	);
+	if (!res.ok) return 0;
+	const data = await res.json();
+	const items = (data.items ?? []) as { user_id?: string; session_id?: string }[];
+	// Deduplicate: prefer user_id when present, fall back to session_id
+	const unique = new Set(items.map((r) => r.user_id || r.session_id || '').filter(Boolean));
+	return unique.size;
+}
+
 /**
  * List replies (1-level deep) for a single parent comment.
  * Always sorted oldest-first so the conversation reads naturally.
@@ -1211,7 +1232,8 @@ export async function createComment(
 	body: string,
 	userId: string | undefined,
 	username: string,
-	parentId?: string
+	parentId?: string,
+	chapter = 0
 ): Promise<PBBookComment> {
 	const token = await getToken();
 	const res = await fetch(`${PB_URL}/api/collections/book_comments/records`, {
@@ -1219,6 +1241,7 @@ export async function createComment(
 		headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' },
 		body: JSON.stringify({
 			slug,
+			chapter,
 			body,
 			user_id: userId ?? '',
 			username,