setup-opds.sh: prompt user to install Docker if not found, using same approach as setup-spoke.sh

hub/setup-opds.sh

@@ -14,7 +14,26 @@ header() { echo -e "\n${CYAN}═════════════════
 
 [ "$(id -u)" -eq 0 ] || die "Run as root"
 
-command -v docker >/dev/null 2>&1 || die "Docker not found. Install Docker first."
+if ! command -v docker >/dev/null 2>&1; then
+    warn "Docker is not installed."
+    read -rp "Install Docker now? [Y/n]: " INSTALL_DOCKER
+    INSTALL_DOCKER="${INSTALL_DOCKER:-y}"
+    if [[ "${INSTALL_DOCKER,,}" == "y" ]]; then
+        header "Installing Docker"
+        if command -v apt-get >/dev/null 2>&1; then
+            apt-get update -q
+            apt-get install -y -q docker.io docker-cli docker-compose
+        else
+            curl -fsSL https://get.docker.com | bash
+        fi
+        if ! command -v docker >/dev/null 2>&1; then
+            die "Docker installation failed."
+        fi
+        info "Docker installed."
+    else
+        die "Docker is required. Aborting."
+    fi
+fi
 
 header "TinyBoard OPDS Setup"
 echo ""