feat: notifications modal, admin dedup, and in-app notification preferences

- Replace bell dropdown with full-screen NotificationsModal (mirrors SearchModal pattern)
- Notifications visible to all logged-in users (not just admin)
- Admin users excluded from new-chapter fan-out (dedup vs Scrape Complete notification)
- Users with notify_new_chapters=false opted out of new-chapter in-app notifications
- Toggle in profile page to enable/disable in-app new-chapter notifications
- PATCH /api/profile endpoint to save notification preferences
- User-facing /notifications page (admin redirects to /admin/notifications)

ui/src/lib/server/pocketbase.ts

@@ -95,6 +95,7 @@ export interface User {
 	oauth_id?: string;
 	polar_customer_id?: string;
 	polar_subscription_id?: string;
+	notify_new_chapters?: boolean;
 }
 
 // ─── Auth token cache ─────────────────────────────────────────────────────────
@@ -1481,6 +1482,25 @@ export async function updateUserAvatarUrl(userId: string, avatarUrl: string): Pr
 	}
 }
 
+/**
+ * Update a user's notification preferences (stored on app_users record).
+ */
+export async function updateUserNotificationPrefs(
+	userId: string,
+	prefs: { notify_new_chapters?: boolean }
+): Promise<void> {
+	const token = await getToken();
+	const res = await fetch(`${PB_URL}/api/collections/app_users/records/${userId}`, {
+		method: 'PATCH',
+		headers: { Authorization: `Bearer ${token}`, 'Content-Type': 'application/json' },
+		body: JSON.stringify(prefs)
+	});
+	if (!res.ok) {
+		const body = await res.text().catch(() => '');
+		throw new Error(`updateUserNotificationPrefs failed: ${res.status} ${body}`);
+	}
+}
+
 // ─── Comments ─────────────────────────────────────────────────────────────────
 
 export interface PBBookComment {