refactor: adopt baby-nas Makefile style with inline packaging targets

- Simplify build targets: frontend, build, build-go, build-all, run, package
- Remove scripts/ for packaging (inline in Makefile)
- Add etc/syncserver/config.yaml and lib/systemd/system/ at project root
- build-all produces both amd64 and arm64 binaries
- package target builds .deb inline without external scripts
- VERSION from git tags, commit hash injected via ldflags

lib/systemd/system/syncserver.service

@@ -0,0 +1,27 @@
+[Unit]
+Description=SyncServer - File sync orchestrator with Wake-on-LAN and web UI
+Documentation=https://github.com/syncserver/syncserver
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=syncserver
+Group=syncserver
+ExecStart=/usr/bin/syncserver --config /etc/syncserver/config.yaml --data-dir /var/lib/syncserver
+Restart=on-failure
+RestartSec=5
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=syncserver
+
+# Hardening
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=strict
+ProtectHome=true
+ReadWritePaths=/var/lib/syncserver /run
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target