Enable passkeys for lszm production

[rzueger]

Enables passkey (WebAuthn) login for lszm production, matching the
existing lszo production setup.

Two parts are required:

1. Config flag (this diff): adds passkeysEnabled: true to the
   lszm production environment in projects/lszm.json. This gates the
   passkey UI in the frontend.

2. GitHub Actions environment variables (already applied to the
   lszm_prod environment, not part of this diff): the WebAuthn Cloud
   Functions require RP config at runtime, otherwise they throw.

   • WEBAUTHN_RPID = lszm.flightbox.aero
   • WEBAUTHN_ORIGINS = https://lszm.flightbox.aero

   WEBAUTHN_RPNAME is intentionally omitted (defaults to Flightbox,
   same as lszo).

No new secrets or infra: the webauthn functions already deploy for
lszm_prod (present in the prod matrix) and challenges use the
existing RTDB.

Deploy note: the prod workflow triggers on push to master, so this
must reach master for passkeys to go live.

Caveat: RPID must exactly match the host users load the app from. If
lszm prod is served on a domain other than lszm.flightbox.aero,
registration/auth will fail and both variables need adjusting.