upstream-tls-verify: Verified TLS to an inbound domain's upstream

Owner, 2026-10-18: "Оба предложения делаем"; the mockup is c10cd78. The
security audit's M7: Required is Postfix's encrypt level, which checks no
certificate - it keeps the mail from a listener, not from one who answers
in the upstream's place.

- A fourth TLS mode, Verified, stored as Postfix's level secure (migration
  0014 rebuilds inbound_transports with the wider CHECK; schema 14) and
  written to the TLS policy map like the others. Postfix matches the
  certificate against the next hop's name (smtp_tls_secure_cert_match =
  nexthop, dot-nexthop, the default; postconf(5)), so Verified is refused
  for an upstream given by address (checkSecureHost).
- Postfix's SMTP client trusts Debian's ca-certificates bundle
  (smtp_tls_CAfile): Postfix trusts none by default (DEF_SMTP_TLS_CA_FILE
  "", DEF_TLS_APPEND_DEF_CA 0). The levels may and encrypt only log the
  verdict, so mail to recipients' MX is unchanged.
- The page: the select's fourth option, a help line under it, the lead
  "over verified TLS", the list's tag "verified"; Help word for word with
  the mockup; guide § Inbound relay, with a posttls-finger command to try
  an upstream first.

Tests: TestVerifiedTLSNeedsTheUpstreamsName, TestRenderInboundMapsSecure,
TestUpstreamTLSModeSecure; schema tests at 14. e2e
inbound_upstream_verified_tls: an address refused, a name saved as
"[sink]:25 secure" in tls_policy, the page says verified, the CA file set
and present, and posttls-finger -l secure with it calls the stand's
self-signed port 25 "Untrusted" (the stand has no TLS upstream). make e2e
(65 passed) and go vet + go test (26 packages) on the test server for this
tree. Tried against the live upstream from the 2.14.5 container:
mc-ent.mixfed.ru gives "Verified TLS connection established".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/migrations/0014_upstream_tls_secure.sql

@@ -0,0 +1,17 @@
+-- The upstream's TLS mode may be 'secure' (upstream-tls-verify, 2.15.0; owner,
+-- 2026-10-18; the security audit of 2026-10-17, M7): Postfix's level that
+-- encrypts and checks the upstream's certificate against its name. The CHECK
+-- of a column cannot be altered in SQLite, so the table is made anew with the
+-- wider one and its rows copied (https://sqlite.org/lang_altertable.html § 7).
+-- Nothing references inbound_transports, so it can be dropped with foreign
+-- keys on; its own reference to inbound_domains goes over with the new table.
+CREATE TABLE inbound_transports_new (
+    inbound_domain_id INTEGER PRIMARY KEY REFERENCES inbound_domains(id) ON DELETE CASCADE,
+    host              TEXT NOT NULL,
+    port              INTEGER NOT NULL CHECK (port >= 1 AND port <= 65535),
+    tls_mode          TEXT NOT NULL CHECK (tls_mode IN ('may', 'encrypt', 'secure', 'none'))
+);
+INSERT INTO inbound_transports_new (inbound_domain_id, host, port, tls_mode)
+    SELECT inbound_domain_id, host, port, tls_mode FROM inbound_transports;
+DROP TABLE inbound_transports;
+ALTER TABLE inbound_transports_new RENAME TO inbound_transports;