docs: add installation guide and deploy:install mise task

- docs/INSTALL.md covers all 6 install methods (local SCP, package install,
  SDK build, official feeds, custom feed, Image Builder/ASU)
- deploy:install mise task: one-command SCP + service restart to an OpenWrt device
  with HOST env var support (default root@192.168.15.1)

mise.toml

@@ -64,3 +64,58 @@ docker exec openwrt-luci sh -c "uci set zt-gateway.global.active_gateway=amsterd
 description = "Full CI: build stack + install browsers + run E2E"
 depends = ["docker:up", "setup"]
 run = "npx playwright test"
+
+
+# ===============================
+# Deployment
+# ===============================
+
+[tasks."deploy:install"]
+description = "SCP app files to an OpenWrt device and restart services"
+run = '''
+set -e
+
+HOST="${HOST:-root@192.168.15.1}"
+
+echo "==> Checking connectivity to ${HOST}..."
+if ! ssh -o ConnectTimeout=5 -o BatchMode=yes "$HOST" true 2>/dev/null; then
+    echo "ERROR: Cannot reach ${HOST}. Check SSH access."
+    echo "  ssh-copy-id ${HOST}  # if needed"
+    exit 1
+fi
+echo "    ${HOST} is reachable."
+
+echo "==> Uploading files..."
+
+# root/ files → strip leading root/, map to / on device
+scp -q root/usr/sbin/zt-gateway-switch                  "$HOST:/usr/sbin/"
+echo "    zt-gateway-switch"
+scp -q root/usr/share/rpcd/ucode/zt-gateway.uc           "$HOST:/usr/share/rpcd/ucode/"
+echo "    rpcd/ucode/zt-gateway.uc"
+scp -q root/usr/share/rpcd/ucode/system.uc               "$HOST:/usr/share/rpcd/ucode/"
+echo "    rpcd/ucode/system.uc"
+scp -q root/usr/share/ucode/luci/runtime.uc              "$HOST:/usr/share/ucode/luci/"
+echo "    ucode/luci/runtime.uc"
+scp -q root/usr/share/luci/menu.d/luci-app-zt-gateway.json   "$HOST:/usr/share/luci/menu.d/"
+echo "    menu.d/luci-app-zt-gateway.json"
+scp -q root/usr/share/rpcd/acl.d/luci-app-zt-gateway.json    "$HOST:/usr/share/rpcd/acl.d/"
+echo "    acl.d/luci-app-zt-gateway.json"
+scp -q root/etc/config/zt-gateway                         "$HOST:/etc/config/"
+echo "    config/zt-gateway"
+
+# Frontend view
+ssh -q "$HOST" mkdir -p /www/luci-static/resources/view/zt-gateway
+scp -q htdocs/luci-static/resources/view/zt-gateway/overview.js  "$HOST:/www/luci-static/resources/view/zt-gateway/"
+echo "    overview.js"
+
+echo "==> Setting permissions..."
+ssh -q "$HOST" chmod +x /usr/sbin/zt-gateway-switch
+
+echo "==> Restarting rpcd and uhttpd..."
+ssh -q "$HOST" /etc/init.d/rpcd restart
+ssh -q "$HOST" /etc/init.d/uhttpd restart
+
+DEVICE_IP=$(echo "$HOST" | sed 's/.*@//')
+echo ""
+echo "==> Done! Open: http://${DEVICE_IP}/cgi-bin/luci/admin/services/zt-gateway"
+'''