docs(e2e): fix stale spec listing after Briefwechsel removal

The e2e README still listed the deleted korrespondenz.spec.ts. Replace it
with the new briefwechsel-removed.spec.ts guard entry — closing the last
dangling reference flagged in review.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/e2e/CLAUDE.md

@@ -25,7 +25,7 @@ frontend/e2e/
 ├── focus-rings.spec.ts        # Accessibility focus ring tests
 ├── header.spec.ts             # Navigation header
 ├── history.spec.ts            # Chronik / activity feed
-├── korrespondenz.spec.ts      # Correspondence timeline
+├── briefwechsel-removed.spec.ts # Guards that the removed /briefwechsel route 404s
 ├── lang.spec.ts               # Language switching
 ├── password-reset.spec.ts     # Password reset flow
 ├── permissions.spec.ts        # Role-based access control