feat(updates): check Gitea automatically and deploy on owner confirmation

Add owner-only update controls, a read-only SSH checker and independent systemd deployment services. Build before maintenance; back up code and database; restore on failed deployment. Preserve runtime configuration and gate business writes during the switch.

deploy/server/systemd/replypier-update.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Install the ReplyPier version explicitly confirmed by its owner
+After=network-online.target docker.service
+Requires=docker.service
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/python3 /opt/replypier-updater/cli.py apply
+ExecStopPost=/usr/bin/python3 /opt/replypier-updater/cli.py recover
+TimeoutStartSec=2h
+TimeoutStopSec=20min
+KillMode=control-group
+UMask=0077
+Nice=10