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.component.form.spec.ts

@@ -143,6 +143,22 @@ describe('SettingsComponent form', () => {
             });
         });
 
+        // The sections are OnPush and a reset or backup import patches the
+        // form outside their template events. A value-only patch changes no
+        // form status signal, so the section must track the value itself.
+        it('re-renders section selections after a value-only form patch', () => {
+            const darkTheme = () =>
+                (fixture.nativeElement as HTMLElement).querySelector(
+                    '[data-test-id="DARK_THEME"]'
+                );
+            expect(darkTheme()?.getAttribute('aria-checked')).toBe('false');
+
+            component.settingsForm.patchValue({ theme: Theme.DarkTheme });
+            fixture.detectChanges();
+
+            expect(darkTheme()?.getAttribute('aria-checked')).toBe('true');
+        });
+
         it('hydrates a shared web controls opt-out from the settings store', () => {
             settingsStore._setSettings({
                 webPlayerSharedControls: false,