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/routes/api/profile/+server.ts

@@ -1,8 +1,43 @@
 import { json, error } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
-import { deleteUserAccount } from '$lib/server/pocketbase';
+import { deleteUserAccount, updateUserNotificationPrefs } from '$lib/server/pocketbase';
 import { log } from '$lib/server/logger';
 
+/**
+ * PATCH /api/profile
+ *
+ * Update mutable profile preferences (currently: notification preferences).
+ * Body: { notify_new_chapters?: boolean }
+ */
+export const PATCH: RequestHandler = async ({ locals, request }) => {
+	if (!locals.user) error(401, 'Not authenticated');
+
+	let body: Record<string, unknown>;
+	try {
+		body = await request.json();
+	} catch {
+		error(400, 'Invalid JSON');
+	}
+
+	const prefs: { notify_new_chapters?: boolean } = {};
+	if (typeof body.notify_new_chapters === 'boolean') {
+		prefs.notify_new_chapters = body.notify_new_chapters;
+	}
+
+	if (Object.keys(prefs).length === 0) {
+		error(400, 'No valid preferences provided');
+	}
+
+	try {
+		await updateUserNotificationPrefs(locals.user.id, prefs);
+	} catch (e) {
+		log.error('profile', 'PATCH /api/profile failed', { userId: locals.user.id, err: String(e) });
+		error(500, { message: 'Failed to update preferences. Please try again.' });
+	}
+
+	return json({ ok: true });
+};
+
 /**
  * DELETE /api/profile
  *