feat: implement personalized background image feature

- Added functionality for users to select and customize background images in settings, including predefined options and URL uploads.
- Updated `ViewPreferences` to store background image settings and modified `userPreferencesService` to handle updates.
- Enhanced global styles for improved readability with background images, including blur and transparency effects.
- Integrated `BackgroundImageSelector` component into settings for intuitive user experience.
- Refactored `Card` components across the app to use a new 'glass' variant for better aesthetics.

src/actions/preferences.ts

@@ -32,6 +32,31 @@ export async function updateViewPreferences(updates: Partial<ViewPreferences>):
   }
 }
 
+/**
+ * Met à jour l'image de fond
+ */
+export async function setBackgroundImage(backgroundImage: string | undefined): Promise<{
+  success: boolean;
+  error?: string;
+}> {
+  try {
+    const session = await getServerSession(authOptions);
+    if (!session?.user?.id) {
+      return { success: false, error: 'Non authentifié' };
+    }
+    
+    await userPreferencesService.updateViewPreferences(session.user.id, { backgroundImage });
+    revalidatePath('/');
+    return { success: true };
+  } catch (error) {
+    console.error('Erreur setBackgroundImage:', error);
+    return {
+      success: false,
+      error: error instanceof Error ? error.message : 'Erreur inconnue'
+    };
+  }
+}
+
 /**
  * Met à jour les filtres Kanban
  */