fix: self-healing permissions on /var/lib/syncserver

- systemd: add ExecStartPre to chown -R the data dir before every start
- postinst: add chown -R after creating dirs to fix ownership on upgrades

This prevents the service from failing if dirs were created by root or
drifted ownership after a manual run.

packaging/debian/DEBIAN/postinst

@@ -10,6 +10,7 @@ case "$1" in
         install -d -o syncserver -g syncserver -m 0750 /var/lib/syncserver/data || true
         install -d -o syncserver -g syncserver -m 0750 /var/lib/syncserver/ssh || true
         install -d -o syncserver -g syncserver -m 0750 /var/lib/syncserver/logs || true
+        chown -R syncserver:syncserver /var/lib/syncserver
         install -d -o root -g root -m 0755 /etc/syncserver || true
 
         if [ ! -f /etc/syncserver/config.yaml ]; then

packaging/debian/lib/systemd/system/syncserver.service

@@ -8,6 +8,7 @@ Wants=network-online.target
 Type=simple
 User=syncserver
 Group=syncserver
+ExecStartPre=/bin/chown -R syncserver:syncserver /var/lib/syncserver
 ExecStart=/usr/bin/syncserver --config /etc/syncserver/config.yaml --data-dir /var/lib/syncserver
 Restart=on-failure
 RestartSec=5