Add "go to last page" and page count to notifications and devices lists

The list endpoints now return a total count alongside the page so the
front-end can show how many pages exist and offer a last-page jump.

Backend: add count(is_new) and count_devices(...) (sharing a WHERE-builder
with list_devices so page and count can't drift), wrap both list responses
in {items, total_count} structs, and register them with utoipa.

Front-end: parse the wrapper shape (dropping the fetch-one-extra trick),
add a Last-page button and a responsive "Page X of Y" / "X / Y" label to
the shared PaginationBar, and track the total in both lists. Notifications
re-sync the count on every fetch and decrement it locally on mark-read/
unread removals so the count stays accurate without a re-fetch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/web_server.rs

@@ -2,8 +2,8 @@ use std::error::Error;
 use std::path::{Path, PathBuf};
 
 use crate::model::device_events::{DeviceEvent, DeviceEventScanner, DeviceEventType};
-use crate::model::devices::{Device, DeviceSummary};
-use crate::model::notifications::{Notification, NotificationType};
+use crate::model::devices::{Device, DeviceListResponse, DeviceSummary};
+use crate::model::notifications::{Notification, NotificationListResponse, NotificationType};
 use crate::settings::get_settings;
 use crate::web_server::devices::{RegisterDevicePayload, UpdateDevicePayload};
 use crate::web_server::scanner_status::{
@@ -66,8 +66,10 @@ pub mod utils;
     ),
     components(schemas(
         Device,
+        DeviceListResponse,
         DeviceSummary,
         Notification,
+        NotificationListResponse,
         NotificationType,
         RegisterDevicePayload,
         UpdateDevicePayload,