Setup polish: optional email verification, standalone landing

[halfcyan]

Part of the Ultramarine Server roadmap (Outline: Server):

dashboard should not expose project/workspace concepts in standalone Ultramarine Server; login should land directly on Hosts
add setup support for optional email verification; default should remain disabled until explicitly enabled

Goal

Two pieces of setup correctness. Email verification: the EMAIL_VERIFICATION_REQUIRED gate exists, but setup never configures a mail provider, so the flag can't be safely turned on. Standalone mode: no project/workspace concepts; login lands on Hosts.

Tasks

• Setup flow gains an optional mail provider step (SMTP settings, send-test-email)
• EMAIL_VERIFICATION_REQUIRED=true only honored after a mail provider is confirmed working; otherwise stays disabled
• Standalone mode: login lands directly on Hosts; project/workspace concepts hidden
• Tests