.env.example: names with a working default are commented (optional), so ovhost validate's from-example check requires only what the service cannot run without

ddiff --git a/.env.example b/.env.example
iindex a614119..51bfdec 100644
---- a/.env.example
++++ b/.env.example
@@@ -30,17 +30,21 @@ BILLING_URL=http://127.0.0.1:4600
  # VIP_BILLING_TIMEOUT_MS=5000
  # Providers offered on plan pages (must be enabled on Billing); `credit` pays from Vibes credit.
  # Leave EMPTY until Billing is authoritative (Wave 8 cutover): checkout is then closed.
--VIP_CHECKOUT_PROVIDERS=
++# optional: unset = 'powerchat,credit'; set but empty = no checkout (before launch)
++# VIP_CHECKOUT_PROVIDERS=
  # Turns Billing's PowerChat checkout_ref into a link: {ref} and {cents}
--VIP_POWERCHAT_LINK_TEMPLATE=
++# optional: empty = no PowerChat link
++# VIP_POWERCHAT_LINK_TEMPLATE=
  # VIP_BILLING_RATES_TTL_MS=300000
  
  # ── Entitlement projection ───────────────────────────────
  # A projection answer is trusted at most this long after VIP last heard from Billing (and never
  # past the paid period's end); within the grace a projection-only check still answers (stale),
  # after it VIP answers "unknown" until Billing confirms.
--VIP_PROJECTION_MAX_AGE_MS=900000
--VIP_PROJECTION_GRACE_MS=60000
++# optional: defaults to 900000
++# VIP_PROJECTION_MAX_AGE_MS=900000
++# optional: defaults to 60000
++# VIP_PROJECTION_GRACE_MS=60000
  
  # ── OpenVibe.Events ──────────────────────────────────────
  # Outbox relay (vip.plan.published, vip.membership.changed); off when empty