Microsoft sign-in no longer fails when the tenant is left unset

An environment variable cannot be null, only empty. The portal chart rendered Authentication__Microsoft__TenantId with an empty default whenever an environment's values did not set one, and the sign-in handler took that empty string as the tenant. The OpenID Connect authority became login.microsoftonline.com//v2.0, its discovery document could never be fetched, and every Microsoft sign-in on that environment ended in a server error — deterministically, on the first request that touched the handler.

Two changes close it. The chart defaults the tenant to organizations, the multi-tenant authority the onboarding guide prescribes; an environment that needs a single tenant still sets its id explicitly. And the portal now treats a blank tenant as unset (falling back to common) instead of building an authority out of it — the Graph sign-in helper in the platform and the Microsoft provider in the portal package alike.