Enable passkeys for lszo test environment

[rzueger]

Turns on the passkeysEnabled flag for the lszo-test environment so
the existing WebAuthn passkey feature becomes available on Luzern-
Beromünster's test site. Production stays off until verified on test.

Prerequisites (done)

• WEBAUTHN_RPID / WEBAUTHN_ORIGINS set on the lszo_test GitHub
  environment (lszo-test.web.app / https://lszo-test.web.app),
  matching the lszm/lszt pattern. The dev workflow writes these into
  functions/.env.lszo-test at deploy time.
• loginForm is already email (required for the passkey button).
• WebAuthn cloud functions and RTDB rules are shared and already
  deployed for lszo.

Verification

• Config merge resolves to passkeysEnabled: true; tsc clean;
  passkey unit tests pass; npm run build --project=lszo bakes the
  flag into the bundle.
• Post-deploy: register a passkey from the profile on
  https://lszo-test.web.app, sign out, sign in with the passkey.

Follow-up

Production enablement is a separate change: add the flag to
environments.production and set the WebAuthn vars on lszo_prod.