Assembly-scanned services, options validator marker, UI tweaks, and config fixes

- Register ISettingsModalService, INotificationService, IUpdateCheckService via assembly scanning (marker interfaces)
- Add IApplicationOptionsValidator<TOptions> marker; scan only those for IValidateOptions registration
- Fix ApplicationLifecycleLoggingHostedService: log RestartCommand/ReloadCommand/StatusCommand (no ApplyCommand)
- NavMenu: spin animation for update-check button icon when checking; single icon with conditional nav-footer-spin class
- Add NotificationHost/NotificationToast components and NotificationService for toasts
- Effective config save flow, restore result, save service; various EffectiveConfig and DnsmasqOptions/validator updates
- Test and script updates; docker-compose.test.yml, appsettings, DnsmasqConfKeys/tooltips/sections

src/DnsmasqWebUI/Components/EffectiveConfig/Modals/EffectiveConfigSaveModal.razor.css

@@ -41,3 +41,21 @@
 .ec-save-modal-empty {
     font-size: 0.9rem;
 }
+
+.ec-save-modal-loading {
+    min-height: 6rem;
+}
+
+.ec-save-modal-backup-path {
+    font-size: 0.9rem;
+}
+
+.ec-save-modal-backup-code {
+    word-break: break-all;
+}
+
+.ec-save-modal-pre {
+    font-size: 0.8125rem;
+    max-height: 12rem;
+    overflow: auto;
+}