Phase 10: deployment (Apache compose + proxy fragments, CI release) + docs

- deploy/docker-compose.yml: pinned-tag ghcr image, hardened (cap_drop ALL +
  minimal cap_add, no-new-privileges, panel bound to 127.0.0.1 only). Apache
  itself runs on the host (spec 10.5), fragment at deploy/apache/.
- Alternative reverse-proxy fragments: nginx (+certbot sidecar), Caddy
  (automatic ACME), Traefik (+acme.json PEM extraction script).
- .github/workflows/release.yml: tag-triggered ghcr.io publish, version piped
  from the git tag into both the binary ldflags and the image tag (spec 10.1).
- Closed a gap from Phase 1: logrotate was installed but never invoked;
  wired up build/logrotate-mail.conf + logrotate-loop.sh + a supervisor
  program (copytruncate, since postlogd holds mail.log open with nothing to
  signal on rotation).
- README rewritten: site requirements checklist, reverse-proxy comparison,
  DNS setup (server- vs domain-level), IP warmup, backup/restore vs domain
  export/import, fixed-tag rationale, machine requirements.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

deploy/traefik/extract-cert.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+# Extracts a PEM cert/key pair for one domain out of Traefik's acme.json
+# (spec 10.3: "Traefik — сертификаты в acme.json, потребуется шаг извлечения
+# PEM"). Run this on the host, after Traefik has issued or renewed the
+# certificate, and again on a schedule (cron/systemd timer) since acme.json
+# is not itself watched by SelfPost/Postfix.
+#
+# Requires jq. Usage: ./extract-cert.sh <acme.json path> <domain> <output dir>
+set -eu
+
+ACME_JSON="${1:?path to acme.json}"
+DOMAIN="${2:?domain name, e.g. mail.example.com}"
+OUT_DIR="${3:?output directory, e.g. ./extracted-certs}"
+
+mkdir -p "$OUT_DIR"
+
+jq -r --arg domain "$DOMAIN" '
+  .le.Certificates[]
+  | select(.domain.main == $domain)
+  | .certificate' "$ACME_JSON" | base64 -d > "$OUT_DIR/fullchain.pem"
+
+jq -r --arg domain "$DOMAIN" '
+  .le.Certificates[]
+  | select(.domain.main == $domain)
+  | .key' "$ACME_JSON" | base64 -d > "$OUT_DIR/privkey.pem"
+
+chmod 0640 "$OUT_DIR/fullchain.pem" "$OUT_DIR/privkey.pem"
+echo "extracted $DOMAIN to $OUT_DIR/{fullchain,privkey}.pem"