#32: file composed mail, and verify DNS records for real

Three things the console and the mail client were getting wrong.

**Sent stayed empty and drafts would not save.** Both write through the same
persistence path, and both failed on the same constraint: spf_result,
dkim_result and dmarc_result are restricted to the RFC verdict vocabulary and
are nullable, so "not evaluated" has to be NULL. The compose path left them at
Go's zero value, which sends an empty string - satisfying neither the CHECK nor
the meaning - and the insert was rejected. Filing the Sent copy is deliberately
non-fatal, so it failed silently; saving a draft reported the error. Inbound
mail was unaffected because it always supplies a real verdict, which is also
why the existing test never caught it.

**DNS reconciliation could not verify anything.** The console posted to the
auth service, which has no resolver, so the endpoint recorded the request and
re-read the status already in the database. The machinery to do it properly
already existed - the background reconciler resolves every expected record
through public resolvers - it just was not reachable from the console.

Adds GET /api/v1/admin/dns/verify to the protocols service, which owns both the
resolver and the record spec, and wires the domains screen to it: every
expected record, its expected value, and whether it actually resolves. A
proxied record is reported as present rather than matching, because behind a
proxy the published answer is the provider's address and comparing values would
always disagree. Reconciliation still runs afterwards so the stored status and
the audit trail stay in step.

The spec is read, never provisioned: opening a screen must not create DKIM keys
as a side effect.

Verified: the persistence test fails without the fix with the exact constraint
violation (email_messages_dkim_result_check), 22 Go packages and 36 webmail
tests green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/OPERATIONS.md

@@ -207,11 +207,6 @@ Being explicit so nothing is assumed:
 - Master key rotation is manual.
 - Log retention is whatever Docker's json-file driver is configured for
   (10 MB × 3 per service, in `docker-compose.yaml`).
-- **Per-record DNS verification is not implemented.** The admin console's
-  reconcile button records the request and re-reads the stored status; it does
-  not query a resolver and compare the thirteen expected records. The console
-  used to draw a table of green ticks for records nobody had checked. Verify by
-  hand, or with `make preflight`, until this is real.
 - **Attachments are not uploaded.** The compose screen lists the files you pick
   and sends their names only; there is no upload endpoint behind the picker
   yet. The screen says so when you attach something, rather than letting the