Fix login output name collision and herregistratie demo eligibility

Walking through the running app surfaced two issues:

- login-form's `submit` output collided with the native DOM `submit` event
  bubbling to <app-login-form>, so login() also fired with an Event (not the
  BSN string) — "bsn.trim is not a function". Renamed the output to `submitted`
  (matching the other forms).
- The static mock herregistratie deadline (2027-09-01) sat outside the 12-month
  eligibility window, so the wizard was correctly hidden. Moved it to 2027-03-01
  so "verloopt binnenkort" is true and the flow is demoable.

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

public/mock/registration.json

@@ -4,5 +4,5 @@
   "beroep": "Arts",
   "registratiedatum": "2012-09-01",
   "geboortedatum": "1985-03-14",
-  "status": { "tag": "Geregistreerd", "herregistratieDatum": "2027-09-01" }
+  "status": { "tag": "Geregistreerd", "herregistratieDatum": "2027-03-01" }
 }