Add first layer complete notification with camera snapshot (#679)

Notify users when the first layer finishes printing so they can check
  adhesion remotely. Triggers once per print when layer 2 begins
  (layer_num >= 2, capped at <= 5 to handle reconnects). Includes a
  camera snapshot attachment. Adds the on_first_layer_complete toggle
  to all notification providers, with backend/frontend/i18n support
  across all 7 locales.

frontend/src/components/NotificationProviderCard.tsx

@@ -158,6 +158,9 @@ export function NotificationProviderCard({ provider, onEdit }: NotificationProvi
             {provider.on_bed_cooled && (
               <span className="px-2 py-0.5 bg-teal-500/20 text-teal-400 text-xs rounded">{t('notifications.bedCooled')}</span>
             )}
+            {provider.on_first_layer_complete && (
+              <span className="px-2 py-0.5 bg-emerald-600/20 text-emerald-300 text-xs rounded">{t('notifications.firstLayer')}</span>
+            )}
             {provider.quiet_hours_enabled && (
               <span className="px-2 py-0.5 bg-indigo-500/20 text-indigo-400 text-xs rounded flex items-center gap-1">
                 <Moon className="w-3 h-3" />
@@ -282,6 +285,17 @@ export function NotificationProviderCard({ provider, onEdit }: NotificationProvi
                   />
                 </div>
 
+                <div className="flex items-center justify-between">
+                  <div>
+                    <p className="text-sm text-white">{t('notifications.firstLayerCompleteLabel')}</p>
+                    <p className="text-xs text-bambu-gray">{t('notifications.firstLayerCompleteDescription')}</p>
+                  </div>
+                  <Toggle
+                    checked={provider.on_first_layer_complete ?? false}
+                    onChange={(checked) => updateMutation.mutate({ on_first_layer_complete: checked })}
+                  />
+                </div>
+
                 <div className="flex items-center justify-between">
                   <p className="text-sm text-white">{t('notifications.printFailed')}</p>
                   <Toggle