Add backups, token expiry warnings and name server checks

- Daily database backups: jarl-backup.timer runs 'jarld backup', which
  writes jarl-<UTC time>.db into backup.dir, checks it before naming it,
  and prunes by the time in the name while always keeping the newest
  keep_at_least. New backup: section in jarl.yaml; the dashboard and
  'jarl status' show the newest backup and warn when it is stale or
  failed. The Debian package enables the timer.
- 'jarld restore [FILE | latest]': checks the backup, shows it next to
  the current database, keeps the current one aside and records the
  restore. 'jarld serve' holds a database lock, so a restore can't run
  under a live jarld and two jarlds can't share a database.
- Token expiry warnings from 14 days ahead: dashboard, token lists, a
  daily log line, and a CLI warning via the Jarl-Token-Expires header;
  'jarl token list --expiring'.
- 'jarl zone serials' and the zone page's Name servers tab: compare the
  serial on a primary zone's secondaries (NS records, also-notify) or a
  secondary zone's primaries with this server's.
- 'jarl zone delegation': for zones on the internet, check the parent's
  delegation and glue against the zone; an undelegated zone gets a note.
- Server: Jarl/<version> header; CLI exit code 2 for failed checks.

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

deploy/systemd/jarl-backup.service

@@ -0,0 +1,47 @@
+# Jarl: one database backup, run daily by jarl-backup.timer.
+# Installed as /etc/systemd/system/jarl-backup.service (see
+# docs/operations.md#backups). What to keep, and where, is in the backup:
+# section of /etc/jarl/jarl.yaml; when it runs is in jarl-backup.timer.
+[Unit]
+Description=Jarl database backup
+Documentation=file:///usr/local/share/doc/jarl/docs/operations.md
+# Nothing to back up before 'jarld init'. (If you moved the database in
+# jarl.yaml, change this with 'systemctl edit jarl-backup.service'.)
+ConditionPathExists=/var/lib/jarl/jarl.db
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/jarld --config /etc/jarl/jarl.yaml backup
+User=jarl
+Group=jarl
+UMask=0077
+Nice=10
+IOSchedulingClass=idle
+
+# The database (read, and the backup's record written) and the backup
+# directory. If you change backup.dir in jarl.yaml, allow the new one too:
+# 'systemctl edit jarl-backup.service' and add ReadWritePaths=/new/dir.
+ProtectSystem=strict
+ReadWritePaths=/var/lib/jarl -/var/backups/jarl
+ProtectHome=yes
+PrivateTmp=yes
+PrivateDevices=yes
+PrivateNetwork=yes
+NoNewPrivileges=yes
+CapabilityBoundingSet=
+AmbientCapabilities=
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectKernelLogs=yes
+ProtectControlGroups=yes
+ProtectClock=yes
+ProtectHostname=yes
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+RestrictAddressFamilies=AF_UNIX
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallErrorNumber=EPERM

deploy/systemd/jarl-backup.timer

@@ -0,0 +1,20 @@
+# Jarl: runs jarl-backup.service (a database backup) every day.
+# Installed as /etc/systemd/system/jarl-backup.timer. Change the schedule
+# with 'systemctl edit jarl-backup.timer', e.g.
+#   [Timer]
+#   OnCalendar=
+#   OnCalendar=*-*-* 02:30
+# and keep backup.warn_after in jarl.yaml above the new interval.
+[Unit]
+Description=Daily Jarl database backup
+Documentation=file:///usr/local/share/doc/jarl/docs/operations.md
+
+[Timer]
+OnCalendar=daily
+# Spread the start over an hour, and catch up on a run missed while the
+# machine was off.
+RandomizedDelaySec=1h
+Persistent=true
+
+[Install]
+WantedBy=timers.target