Reconcile docs with shipped features: subscriptions, merchant profiles, no email

payments.md: flag the smtp_* columns dormant and the companion email plan superseded. HOW_IT_WORKS.md predated recurring subscriptions and merchant profiles -- correct 'not a subscription service' (subscriptions ship on paid tiers), the single-tenant / one-box-one-business framing (merchant profiles let one instance host multiple businesses), and the 'short of an email' aside (Keysat never emails keys).

docs/guides/payments.md

@@ -17,8 +17,10 @@ paths:
 
 # Payments & the multi-provider / merchant-profile model
 
-Full design spec: `plans/multi-provider-payment-model.md`. Companion email plan:
-`plans/keysat-smtp-emails.md`.
+Full design spec: `plans/multi-provider-payment-model.md`. The companion email
+plan `plans/keysat-smtp-emails.md` is **superseded** — Keysat does not send email;
+operators receive events via webhooks and run their own email pipelines (see the
+"Operability & alerts" item in `ROADMAP.md`).
 
 ## Model
 
@@ -32,7 +34,8 @@ merchant_profiles (1) ──< (N) payment_providers
 ```
 
 - **merchant_profiles** — business identity: name, branding, post-purchase
-  redirect, optional per-profile SMTP override fields. Exactly one `is_default`,
+  redirect. (The `smtp_*` columns from migration 0020 are **dormant** — never read
+  by any send path; the email plan was dropped.) Exactly one `is_default`,
   auto-created at first boot from the operator-name setting.
 - **payment_providers** — one row per configured BTCPay/Zaprite account, attached
   to a profile (`kind` ∈ `btcpay`|`zaprite`).