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>

frontend/test/widget/pagination_bar_test.dart

@@ -1,12 +1,16 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:frontend/theme/dimens.dart';
 import 'package:frontend/theme/gruvbox_theme.dart';
 import 'package:frontend/widgets/pagination_bar.dart';
 
 void main() {
-  Widget wrap(Widget child) => MaterialApp(
-    theme: gruvboxDarkTheme,
-    home: Scaffold(body: child),
+  Widget wrap(Widget child, {Size? size}) => MediaQuery(
+    data: MediaQueryData(size: size ?? const Size(1200, 800)),
+    child: MaterialApp(
+      theme: gruvboxDarkTheme,
+      home: Scaffold(body: child),
+    ),
   );
 
   testWidgets('disables every navigation button while loading', (tester) async {
@@ -15,7 +19,7 @@ void main() {
       wrap(
         PaginationBar(
           currentPage: 1,
-          hasNextPage: true,
+          totalPages: 3,
           isLoading: true,
           onPageChanged: (page) => changedTo = page,
         ),
@@ -25,6 +29,7 @@ void main() {
     await tester.tap(find.byTooltip('Next page'));
     await tester.tap(find.byTooltip('Previous page'));
     await tester.tap(find.byTooltip('First page'));
+    await tester.tap(find.byTooltip('Last page'));
     expect(changedTo, -1);
   });
 
@@ -34,7 +39,7 @@ void main() {
       wrap(
         PaginationBar(
           currentPage: 1,
-          hasNextPage: true,
+          totalPages: 3,
           isLoading: false,
           onPageChanged: (page) => changedTo = page,
         ),
@@ -47,4 +52,73 @@ void main() {
     await tester.tap(find.byTooltip('Previous page'));
     expect(changedTo, 0);
   });
+
+  testWidgets('last-page button jumps to the final page', (tester) async {
+    var changedTo = -1;
+    await tester.pumpWidget(
+      wrap(
+        PaginationBar(
+          currentPage: 0,
+          totalPages: 5,
+          isLoading: false,
+          onPageChanged: (page) => changedTo = page,
+        ),
+      ),
+    );
+
+    await tester.tap(find.byTooltip('Last page'));
+    expect(changedTo, 4);
+  });
+
+  testWidgets('forward buttons disable on the last page', (tester) async {
+    var changedTo = -1;
+    await tester.pumpWidget(
+      wrap(
+        PaginationBar(
+          currentPage: 4,
+          totalPages: 5,
+          isLoading: false,
+          onPageChanged: (page) => changedTo = page,
+        ),
+      ),
+    );
+
+    await tester.tap(find.byTooltip('Next page'));
+    await tester.tap(find.byTooltip('Last page'));
+    expect(changedTo, -1);
+  });
+
+  testWidgets('spells out the page label on wide layouts', (tester) async {
+    await tester.pumpWidget(
+      wrap(
+        const PaginationBar(
+          currentPage: 1,
+          totalPages: 5,
+          isLoading: false,
+          onPageChanged: _noop,
+        ),
+        size: const Size(1200, 800),
+      ),
+    );
+
+    expect(find.text('Page 2 of 5'), findsOneWidget);
+  });
+
+  testWidgets('uses the compact page label on narrow layouts', (tester) async {
+    await tester.pumpWidget(
+      wrap(
+        const PaginationBar(
+          currentPage: 1,
+          totalPages: 5,
+          isLoading: false,
+          onPageChanged: _noop,
+        ),
+        size: Size(Breakpoints.medium - 1, 800),
+      ),
+    );
+
+    expect(find.text('2 / 5'), findsOneWidget);
+  });
 }
+
+void _noop(int _) {}