inbound-antispam-panel: inbound journal milter on port 25

Step 3/12 of docs/plans/inbound-antispam-panel.md.

The panel serves a second milter while the inbound relay is on
(internal/milter/inbound.go, socket INBOUND_JOURNAL_MILTER_SOCKET,
default /run/selfpost/inbound-journal.sock). build/postfix-config.sh
puts it last on port 25, after the optional antispam milter, with
default_action=accept; postfix-wrapper.sh waits for its socket. At
end-of-message it writes one inbound_spam_log row per recipient at an
inbound domain - other port-25 recipients (DMARC report addresses) get
none - and always accepts. With a filter attached it reads the verdict
from X-Rspamd-Action and X-Spamd-Result (action, score, up to six
weighted symbols, only what the patterns recognise, 255 bytes); without
one those headers are the sender's and are not read. The plan named
X-Rspamd-Score, which rspamd does not have.

The antispam compose fragment mounts rspamd/milter_headers.conf into
the sidecar so that it adds the two headers (checked in rspamd 3.11:
both routines exist and remove a sender's own headers of those names).

Store: InsertInboundSpam, IsInboundDomain.

Checked on the test server, uncommitted tree: go vet ./... ok,
go test ./... ok (22 packages), make e2e ok - the relayed message of
inbound_relay_delivers_and_refuses has its journal row (accept by
selfpost) and the DMARC report sent through the same listener has none.

Not yet seen in a real run: a verdict written by rspamd reaching this
milter. The e2e stand has no filter, and the test server's only inbound
domain has no upstream, so it accepts no mail.

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

CHANGELOG.md

@@ -10,7 +10,22 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 - Schema: migration `0002_inbound_spam_log.sql`, the first after the 2.0
   baseline - two empty tables for the inbound antispam journal and the filter
   lists (inbound-antispam-panel). A 2.0.x database is migrated when the panel
-  starts; nothing reads or writes the tables yet.
+  starts.
+- **Inbound mail is recorded.** With the inbound relay on, the panel runs a
+  second milter, the last one on port 25, and writes a row for every recipient
+  of a message that was accepted for an inbound domain: client address,
+  envelope, subject and - with a spam filter attached - the filter's action,
+  score and heaviest symbols. It only watches: it refuses nothing and Postfix
+  accepts mail when it is down. Refused mail is not there yet (it comes from
+  the mail log, next), and there is no page for the journal yet.
+- The antispam compose fragment mounts `antispam/rspamd/milter_headers.conf`
+  into the rspamd sidecar, which makes it write its verdict into
+  `X-Rspamd-Action` and `X-Spamd-Result`. **Copy `deploy/antispam/rspamd/`
+  next to the fragment before starting it** - Docker creates a directory in
+  place of a missing file and the sidecar then fails to read its
+  configuration.
+- New setting `INBOUND_JOURNAL_MILTER_SOCKET` (default
+  `/run/selfpost/inbound-journal.sock`).
 
 ## [2.0.1] - 2026-10-11