perf(web): add an opt-in zoneless change-detection build flag (#1824)

* perf(web): add an opt-in zoneless change-detection build flag

Plan item C6 step 4. app.config.ts takes its change-detection providers
from environments/change-detection.providers.ts, which keeps
provideZoneChangeDetection({ eventCoalescing: true }) for every existing
build. The new electron-performance-zoneless and electron-e2e-zoneless
web configurations are their base configuration plus one fileReplacements
swap to provideZonelessChangeDetection(), so the journeys and the Electron
E2E suite can run zoneless while nothing ships it. zone.js stays in the
polyfills until the flip.

A build-config test pins each *-zoneless configuration to its base plus
the swap and refuses the swap anywhere else.

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

* fix(epg): schedule the guide's post-render scroll without zone.js

The programme guide jumps to now once the virtual list first renders rows,
and focuses cells after keyboard scrolls, from afterNextRender hooks
registered in CDK and RxJS callbacks. zone.js followed those callbacks
with a tick; under zoneless change detection a render hook schedules no
render, so the guide opened at midnight (epg-guide.e2e.ts on the zoneless
build). The guide now marks itself when it registers one, which is
harmless with zone.js.

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

* docs(performance): record the zoneless flag measurements and E2E run

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

* docs(performance): say the zoneless flag ran with the three implemented journeys

Review follow-up (Greptile): J4 search is still planned, so the flag was
validated with J1-J3 and the Electron E2E suite, not all four journeys.

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

---------

Co-authored-by: 4gray <fourgray@proton.me>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

apps/electron-backend-e2e/src/performance/performance-build-config.spec.ts

@@ -10,6 +10,7 @@ import { JOURNEY_CD_TICK_COUNTER_KEY } from './journey-renderer-probe';
 
 interface TargetConfiguration {
     configurations?: Record<string, Record<string, unknown>>;
+    defaultConfiguration?: string;
     dependsOn?: unknown;
     executor?: unknown;
     options?: Record<string, unknown>;
@@ -162,7 +163,12 @@ test('only the web performance build installs the tick counter the journeys read
     for (const [name, configuration] of Object.entries(
         webProject.targets['build'].configurations ?? {}
     )) {
-        if (name === 'electron-performance') continue;
+        if (
+            name === 'electron-performance' ||
+            name === 'electron-performance-zoneless'
+        ) {
+            continue;
+        }
         assert.doesNotMatch(
             JSON.stringify(configuration['fileReplacements'] ?? []),
             /environment\.performance/,
@@ -171,6 +177,44 @@ test('only the web performance build installs the tick counter the journeys read
     }
 });
 
+// Plan item C6 measures zoneless change detection behind a build-time flag:
+// each *-zoneless configuration is its base configuration plus one swap of
+// the change-detection providers, and nothing else selects that swap.
+test('the zoneless flag is opt-in through the *-zoneless web configurations only', () => {
+    const configurations = webProject.targets['build'].configurations ?? {};
+    const zonelessReplacement = {
+        replace: 'apps/web/src/environments/change-detection.providers.ts',
+        with: 'apps/web/src/environments/change-detection.providers.zoneless.ts',
+    };
+
+    for (const base of ['electron-performance', 'electron-e2e']) {
+        const baseConfiguration = configurations[base];
+        const zoneless = configurations[`${base}-zoneless`];
+        assert.ok(zoneless, `web:build must define ${base}-zoneless`);
+        assert.ok(baseConfiguration, `web:build must define ${base}`);
+        const { fileReplacements: baseReplacements, ...baseRest } =
+            baseConfiguration;
+        const { fileReplacements, ...rest } = zoneless;
+        assert.deepEqual(rest, baseRest, base);
+        assert.deepEqual(fileReplacements, [
+            ...((baseReplacements as unknown[] | undefined) ?? []),
+            zonelessReplacement,
+        ]);
+    }
+    for (const [name, configuration] of Object.entries(configurations)) {
+        if (name.endsWith('-zoneless')) continue;
+        assert.doesNotMatch(
+            JSON.stringify(configuration['fileReplacements'] ?? []),
+            /change-detection\.providers/,
+            name
+        );
+    }
+    assert.equal(
+        webProject.targets['build'].defaultConfiguration,
+        'production'
+    );
+});
+
 test('the resolved web build cache output is the renderer directory', () => {
     const task = readResolvedWebBuildTask();