e2e: full backup from the panel, restore into an empty directory

After the rate-limit checks the run takes a full backup through the
panel, reads the archive through while the container can still say what
went wrong, then removes data/, certs/, docker-compose.yml and .env,
unpacks the archive into the project directory, puts the private key
back (the panel's archive comes without it and without the queue, both
asserted), and starts the stand again.

What has to hold: manifest.json is consumed by the first start, the
administrator signs in, the domain shows the same DKIM value, and a
message sent with the application's old password reaches the sink and
verifies against the record published before the backup.

The port-25 scenarios then run on the restored installation.

make e2e on the test server: ok.

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

CHANGELOG.md

@@ -19,6 +19,20 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 - DMARC reports are kept 500 **for each domain** (and 90 days), not 500 for
   the whole server - see Security.
 
+### Fixed
+
+- **Full backup from the panel works.** Since the Postfix queue moved under
+  `/data` in 1.3.0 the button answered with a 200 and ten bytes: the archive
+  includes the queue, Postfix keeps the queue readable by its own user alone,
+  and the panel is not that user ("open /data/postfix/queue/active:
+  permission denied" in the log). `selfpost-backup` run with `docker exec`
+  was not affected - it runs as root. The panel's archive now leaves the queue
+  out, and likewise a file in `certs/` it may not open (usually the private
+  key, named in the log); the page, Help and the guide say so, and the guide
+  says to put the key back before starting a restored instance. Everything is
+  read through before the download starts, so a failure is a message on the
+  page and not a file cut short.
+
 ### Security
 
 Review of the DMARC report path (Fable, 2026-10-11), which started to run for
@@ -49,6 +63,11 @@ the first time in 2.0.0. Nothing Critical or High.
   report are accepted and dropped; mail for an inbound domain reaches its
   upstream and other recipients are refused. Until now the suite only read
   back the generated configuration of these features.
+- e2e: full backup and restore. The run takes a backup from the panel, throws
+  the installation away, unpacks the archive into the empty project directory
+  and starts it: the administrator signs in, the domain has the same DKIM key,
+  and mail sent by the application verifies against the record published
+  before the backup.
 
 ## [2.0.0] - 2026-10-11