CreateTenant now defaults trial_ends_at to NOW() + 14 days when the
new tenant lands in status='trial'. Demo-kind tenants get
status='demo' (per PLATFORM_ARCHITECTURE.md §5d) and trial_ends_at
stays NULL — those flow through the M13.2 demo-provisioning path.
Both store implementations (Memory + Postgres) updated; tests assert
the 14-day window for customers and the absent end for demo kind.
Unblocks M12.1 (portal trial banner can render a real countdown).
Refs: M4.1 + M12.1
sharang
ad0b2ef949