fix(entrypoint): make /data traversable; hostname gate first (v1.0.0)

Go TempDir bind mounts arrive as 0700; after chown panel:panel, OpenDKIM
could not reach KeyTable and the container crash-looped. chmod 755 /data,
check SELFPOST_HOSTNAME before /data setup, and harden the e2e stand
(restart: no, readiness logs).

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

CHANGELOG.md

@@ -32,6 +32,12 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ### Fixed
 
+- Entrypoint: check `SELFPOST_HOSTNAME` before `/data` setup (so a bad identity
+  fails with the FATAL text, not an earlier `set -e` abort), and `chmod 755
+  /data` after chown so OpenDKIM/Postfix can traverse bind mounts that arrive
+  as mode `0700` (Go `TempDir`, some host umasks) — otherwise KeyTable is
+  unreachable and the container crash-loops. E2e stand uses `restart: "no"` and
+  surfaces selfpost logs from the supervisor readiness check.
 - E2e gate: wait for host-published `/healthz` before panel setup, and stop
   ordered `TestE2E` subtests after a failure so a nil panel client cannot panic
   and mask the real error (release CI on both amd64 and arm64).