fix(e2e): read setup-token via exec; reclaim /data

Container startup is green; CI failed because panel-owned setup-token (0600)
was unreadable on the host bind mount, and TempDir cleanup hit EACCES on
sqlite/opendkim files. Read the token with compose exec (as guide.md) and
chown /data before removing containers/stage.

Co-Authored-By: Composer <noreply@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

CHANGELOG.md

@@ -16,6 +16,10 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   master.cf service. After mail.log moved to `/data/log`, `postfix check`
   fatally rejected the path (default prefixes are only `/var` and
   `/dev/stdout`) and often left stderr/mail.log empty.
+- e2e: read `/data/setup-token` via `docker compose exec` (file is `0600`
+  panel-owned; host `ReadFile` got permission denied on CI). Reclaim `/data`
+  ownership before TempDir/stage cleanup so panel/postfix UIDs do not fail
+  Go's `RemoveAll`.
 
 ## [1.0.0] - 2026-08-09