perf(web): make the app root and settings components OnPush

Plan item C6 step 3 for apps/web: the fifteen Eager components switch to
OnPush, among them the app root and the update notification panel that
the idle audit found re-rendering on every idle tick. Their template
state is signals from the settings facades, signal inputs and the shared
reactive settings form.

The checklist flagged the backup import, which patches the form from a
detached file input with no template event. A new spec patches only a
value, which changes no form status, and confirms the OnPush general
section still shows the new theme; it guards that path for the zoneless
flag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/app/settings/settings-general-section.component.ts

@@ -33,8 +33,7 @@ import {
     ],
     templateUrl: './settings-general-section.component.html',
     encapsulation: ViewEncapsulation.None,
-    // eslint-disable-next-line @angular-eslint/prefer-on-push-component-change-detection -- Preserve pre-Angular 22 eager checking during the framework upgrade.
-    changeDetection: ChangeDetectionStrategy.Eager,
+    changeDetection: ChangeDetectionStrategy.OnPush,
     styles: [':host { display: contents; }'],
 })
 export class SettingsGeneralSectionComponent {