fix(e2e): fix WebAuthn and integration test failures

- Use localhost instead of 127.0.0.1 as TARGET_URL so the WebAuthn RP ID
  is a valid domain (the spec forbids IP addresses)
- Replace request.post('/logout') with page.context().clearCookies() since
  Playwright's request fixture has a separate cookie jar from the page
- Add registerPasskey() helper that waits for 'load' event to reliably
  detect the page reload after successful registration
- Track credential count with getCredentialCount() since credentials
  accumulate across serial tests sharing the same database
- Fix login.spec.js selector from #webauthn-login-form to #webauthn-login-btn
  to match the actual template

All 57 E2E tests now pass (50 migrated + 7 WebAuthn).

tests/e2e/run.sh

@@ -14,7 +14,9 @@ SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 PROJECT_ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
 
 PORT="${E2E_PORT:-8099}"
-export TARGET_URL="http://127.0.0.1:${PORT}"
+# Use "localhost" (not 127.0.0.1) so that the WebAuthn RP ID is a valid
+# domain — the spec forbids IP addresses as RP IDs.
+export TARGET_URL="http://localhost:${PORT}"
 
 # --- Temp directory for e2e state ---
 E2E_TMPDIR="$(mktemp -d)"