test(lighthouse-react): Use static imports gated by MODE for tree-shaking (#21030)

## Summary

Replace the dynamic `await import('./sentry/<mode>')` branching in
`main.tsx` with a single static `import * as Sentry from
'@sentry/react'` guarded by `import.meta.env.MODE`. This more closely
mirrors what a real consumer app looks like: a static SDK import at the
top, with `Sentry.init()` called conditionally. The build matrix still
produces three distinct bundles via `vite build --mode <mode>`, but the
code path is now realistic instead of a code-splitting trick.

## How tree-shaking handles each mode

Vite inlines `import.meta.env.MODE` as a string literal at build time.
Rollup then eliminates dead `if` branches, and `@sentry/react`'s
`"sideEffects": false` lets the namespace import be tree-shaken away
entirely when no member is referenced.

- **`no-sentry`**: both branches are statically dead → `Sentry.*`
unreferenced → the entire `@sentry/react` import is dropped from the
bundle.
- **`init-only`**: only `Sentry.init({ enabled: false })` survives;
`browserTracingIntegration` / `replayIntegration` are tree-shaken.
- **`tracing-replay`**: full SDK + tracing + replay.

## Verified bundle output

| Mode | Bundle | Sentry SDK symbols¹ |
|---|---|---|
| `no-sentry` | 144 KB | 0 |
| `init-only` | 229 KB (+85 KB) | present |
| `tracing-replay` | 418 KB (+274 KB) | 7 |

¹ Count of `captureException` / `startSpan` / `getCurrentScope` /
`__SENTRY__` / `sentry-trace` occurrences in the output JS. The only
`Sentry` literal in the `no-sentry` bundle is the marketing copy string
in `App.tsx`, not SDK code.

The per-mode helper files in `src/sentry/` are no longer needed and have
been deleted.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mydea

dev-packages/e2e-tests/test-applications/lighthouse-react/src/main.tsx

@@ -1,20 +1,24 @@
+import * as Sentry from '@sentry/react';
 import { createRoot } from 'react-dom/client';
 import App from './App';
 
-async function bootstrap() {
-  const mode = import.meta.env.MODE;
-  if (mode === 'init-only') {
-    const { initSentry } = await import('./sentry/init-only');
-    initSentry();
-  } else if (mode === 'tracing-replay') {
-    const { initSentry } = await import('./sentry/tracing-replay');
-    initSentry();
-  }
-  // 'no-sentry' mode: do not import any sentry module — the dynamic-import
-  // branches above are unreachable and Vite drops them from the bundle.
-
-  const root = createRoot(document.getElementById('root')!);
-  root.render(<App />);
+if (import.meta.env.MODE === 'tracing-replay') {
+  Sentry.init({
+    dsn: import.meta.env.VITE_E2E_TEST_DSN as string | undefined,
+    release: 'lighthouse-fixture',
+    environment: 'qa',
+    integrations: [Sentry.browserTracingIntegration(), Sentry.replayIntegration()],
+    tracesSampleRate: 1.0,
+    replaysSessionSampleRate: 1.0,
+    replaysOnErrorSampleRate: 1.0,
+  });
+} else if (import.meta.env.MODE === 'init-only') {
+  // enabled: false makes the SDK a guaranteed no-op (no transport allocation,
+  // no DSN warning). We're measuring pure SDK-loading + tree-shaking cost.
+  Sentry.init({ enabled: false });
 }
+// 'no-sentry' mode: both branches above are statically dead, so Vite drops
+// the @sentry/react import entirely from the bundle.
 
-void bootstrap();
+const root = createRoot(document.getElementById('root')!);
+root.render(<App />);