feat: notification system via Mercure for scraping events

- NotificationInterface: add sendInfo() and sendWarning() levels
- SymfonyNotification: implement new levels (publishes to 'notifications' topic)
- ChapterScrapingStarted: carry mangaTitle + chapterNumber, now dispatched
- ScrapeChapterHandler: dispatch ChapterScrapingStarted before scraping loop
- ScrapingEventSubscriber: wire NotificationInterface for started/scraped/failed events
- useMercureNotifications: new global Vue composable subscribing to 'notifications' topic
- App.vue: mount useMercureNotifications() at app root
- SendTestNotificationCommand: `app:notify:test --type --message` for dev/prod testing

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

assets/vue/app/App.vue

@@ -5,6 +5,9 @@
 
 <script setup>
 import NotificationToast from './shared/components/ui/NotificationToast.vue';
+import { useMercureNotifications } from './shared/composables/useMercureNotifications';
+
+useMercureNotifications();
 </script>
 
 <style>

assets/vue/app/shared/composables/useMercureNotifications.js

@@ -0,0 +1,45 @@
+import { onMounted, onBeforeUnmount } from 'vue';
+import { useNotifications } from './useNotifications';
+
+export function useMercureNotifications() {
+    const { showSuccess, showError, showInfo, showWarning } = useNotifications();
+    let eventSource = null;
+
+    const handleNotification = data => {
+        const message = data.message ?? 'Notification';
+        switch (data.status) {
+            case 'success': showSuccess(message); break;
+            case 'error':   showError(message);   break;
+            case 'warning': showWarning(message); break;
+            default:        showInfo(message);
+        }
+    };
+
+    const setup = () => {
+        const url = new URL('/.well-known/mercure', window.location.origin);
+        url.searchParams.append('topic', 'notifications');
+
+        eventSource = new EventSource(url, { withCredentials: true });
+
+        eventSource.onmessage = event => {
+            try {
+                const data = JSON.parse(event.data);
+                handleNotification(data);
+            } catch (e) {
+                console.error('useMercureNotifications: erreur de parsing', e);
+            }
+        };
+
+        eventSource.onerror = () => {
+            eventSource?.close();
+            setTimeout(setup, 5000);
+        };
+    };
+
+    onMounted(setup);
+
+    onBeforeUnmount(() => {
+        eventSource?.close();
+        eventSource = null;
+    });
+}