release: 2.7.0: base-trixie - Debian trixie, Postfix 3.10.13

Cut without asking, as the owner said on 2026-10-15.

The image runs debian:trixie-slim with Postfix 3.10.13, libmilter
8.18.1, OpenSSL 3.5; every citation re-read against the trixie sources.
smtpd_hide_client_session=yes on 465/587 (owner's decision). The
selfpost group is 10998 and the panel 10999:10999, outside the system
range; the entrypoint re-owns /data by name. The panel's database is
0600; the entrypoint removes symbolic links the panel could leave under
/data. Commits 68ec8b2, 1c6e04b, a3050af.

Rolled out to the test server as 2.6.1-post.a3050af (the same code),
2026-10-15 17:07 UTC: healthy, every program RUNNING, no restarts, three
messages sent, the queue empty, no warning but outside password guessing.
The canary: one message from an application through 465 to Gmail, Yandex
and the test mailbox - Received: in the short form everywhere; Gmail
dkim=pass spf=pass dmarc=pass; Yandex spf=pass dkim=pass, not spam.
No migration, schema 11.

CHANGELOG cut; pin 2.7.0 in deploy/docker-compose.yml, README, guide (and
its sample restore message); development.md "from pin" and the rows of
base-trixie and panel-dkim-signing; roadmap row and recommended order.
No tag.

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

README.md

@@ -112,8 +112,8 @@ outbound mail will not reach the real internet without DNS, PTR, and port 25.
 > local image and pulls nothing:
 >
 > ```sh
-> docker build -f build/Dockerfile --build-arg VERSION=2.6.1 \
->   -t ghcr.io/mixeme/selfpost:2.6.1 .
+> docker build -f build/Dockerfile --build-arg VERSION=2.7.0 \
+>   -t ghcr.io/mixeme/selfpost:2.7.0 .
 > ```
 
 ```sh
@@ -122,7 +122,7 @@ docker run --rm -d --name selfpost-try \
   -e SELFPOST_HOSTNAME=mail.local.test \
   -e PANEL_COOKIE_SECURE=false \
   -v selfpost-try-data:/data \
-  ghcr.io/mixeme/selfpost:2.6.1
+  ghcr.io/mixeme/selfpost:2.7.0
 ```
 
 **Get the setup URL** (pick one):