fix(backup): reimport postgres dump on restore (restore was a no-op)

The db service dumped the DB on backup (pg_dump pre-hook) but shipped no
restore hook, and a file-level restore does not reload into the running
postgres, so a restored backup silently kept the live (un-restored) state.
Add pg_backup.sh (backup=pg_dump|gzip into the postgresql_data volume;
restore=terminate conns + DROP DATABASE WITH FORCE + createdb + reimport),
mount it via a config, and wire the backupbot backup/restore hooks. Same
fix as the immich / mattermost-lts / ghost recipes.

compose.yml

@@ -49,7 +49,7 @@ services:
       interval: 30s
       timeout: 10s
       retries: 6
-      start_period: "${APP_START_PERIOD:-5m}"
+      start_period: ${APP_START_PERIOD:-5m}
 
   db:
     image: postgres:13