test: lock journey lifecycle and static fallback

tests/browser/README.md

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+# Browser characterization tests
+
+These Playwright tests lock the observable portfolio behavior at the browser
+boundary. They exercise the built `dist/` output through the local preview
+server rather than replacing Vue, Three.js, WebGL, or Web Audio with production
+test hooks.
+
+## Run
+
+Build the preview artifacts, then run the whole browser suite:
+
+```bash
+npm run build:preview
+npm run test:browser
+```
+
+Run only the Phase 2 journey gate:
+
+```bash
+npm run test:browser -- tests/browser/journey-integration.spec.ts tests/browser/reduced-motion.spec.ts tests/browser/static-fallback.spec.ts tests/browser/bfcache-lifecycle.spec.ts
+```
+
+## Add a case
+
+1. Name the concrete regression the case catches.
+2. Use literal inputs and expected browser-visible results.
+3. Install `scene-instrumentation.ts` before navigation when resource counts or
+   platform calls are the observable boundary.
+4. Keep failure injection in `page.addInitScript()` or Playwright routing; do
+   not add a test API to the application bundle.
+5. Run the new case against both configured Chromium profiles, then run the
+   full suite.
+
+Never copy credentials, private project identifiers, or private URLs into a
+fixture. Use clearly fake values when a credential-shaped input is required.