feat(packaging): add user-mode systemd service for squall-web

Mirrors the existing user squalld.service so squall-web can be run as a
per-user unit alongside it, rather than only the system-wide service.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: flound1129

debian/squall-web.install

@@ -1 +1,2 @@
 packaging/systemd/squall-web.service lib/systemd/system
+packaging/systemd/user/squall-web.service usr/lib/systemd/user

packaging/systemd/user/squall-web.service

@@ -0,0 +1,23 @@
+[Unit]
+Description=Squall Bittorrent Client Web Interface
+Documentation=man:squall-web
+After=squalld.service
+Wants=squalld.service
+
+[Service]
+Type=simple
+UMask=027
+
+ExecStart=/usr/bin/squall-web -d
+Restart=on-failure
+Slice=background.slice
+
+NoNewPrivileges=yes
+PrivateTmp=yes
+ProtectSystem=full
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectControlGroups=yes
+
+[Install]
+WantedBy=default.target