fix(plugin-multi-tenant): prevent form reset when tenant create fails validation

[jhjh1214]

What?

When creating a document in the tenants collection, a client-side validation failure caused the entire form to wipe its values.

Why?

WatchTenantCollection watches submitted and calls syncTenants() whenever operation === 'create' && submitted. But submitted becomes true on any submit attempt — including failed validation — not only on a successful save. The resulting syncTenants() call triggered a state cascade that called router.refresh(), which reset the form to its empty initial state.

How?

Added an id guard to the effect:

if (operation === 'create' && submitted && id) {

Fixes #16953