feat(deploy): nightly database backups with verified restore (M7)

A backup container dumps the database every night, keeps 14 daily and 8 weekly
copies and once a week restores a copy into a scratch database to check tables
and row counts. update.sh takes a copy before updating, restore.sh brings one
back and keeps the old database aside. CI runs the dump, verify and restore
cycle on the database the end-to-end journey filled.

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

deploy/update.sh

@@ -53,6 +53,12 @@ if [ -n "$cur_core" ] && [ -n "$tgt_core" ] && [ "$cur_core" != "$tgt_core" ] &&
   fi
 fi
 
+# Копия базы перед обновлением: миграции назад не откатываются (deploy/restore.sh — вернуть).
+if [ -n "$(docker compose ps -q --status running postgres 2>/dev/null)" ]; then
+  echo "→ резервная копия базы"
+  docker compose run --rm --no-deps backup once >/dev/null
+fi
+
 echo "→ переключаемся на $REF"
 if git show-ref --verify --quiet "refs/remotes/origin/$REF"; then
   git checkout --quiet "$REF"