feat: Add companion agent one-click deployment + fix frontend TS errors

Go deployment orchestrator with platform-specific SteamCMD install,
Rust server download, server.cfg generation, and service registration.
Wire deploy command subscription in daemon, make GameServerPath optional,
add InstallDir config with OS-aware defaults. Fix unused imports and
WebSocket subscribe API in ServerView.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

companion-agent/internal/deploy/deploy_linux.go

@@ -0,0 +1,127 @@
+//go:build linux
+
+package deploy
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+// InstallSteamCMD downloads and installs SteamCMD for Linux into the given
+// install directory. If SteamCMD is already present it returns the existing
+// path without re-downloading. The returned string is the absolute path to
+// the steamcmd.sh executable.
+func InstallSteamCMD(installDir string) (string, error) {
+	steamcmdDir := filepath.Join(installDir, "steamcmd")
+	steamcmdPath := filepath.Join(steamcmdDir, "steamcmd.sh")
+
+	// Already installed — nothing to do.
+	if _, err := os.Stat(steamcmdPath); err == nil {
+		log.Printf("SteamCMD already installed at %s", steamcmdPath)
+		return steamcmdPath, nil
+	}
+
+	if err := os.MkdirAll(steamcmdDir, 0755); err != nil {
+		return "", fmt.Errorf("failed to create steamcmd directory %s: %w", steamcmdDir, err)
+	}
+
+	// Download the Linux tarball.
+	tarball := filepath.Join(steamcmdDir, "steamcmd_linux.tar.gz")
+	if err := downloadFile("https://steamcdn-a.akamaihd.net/client/installer/steamcmd_linux.tar.gz", tarball); err != nil {
+		return "", fmt.Errorf("failed to download steamcmd: %w", err)
+	}
+
+	// Extract with tar.
+	cmd := exec.Command("tar", "-xzf", "steamcmd_linux.tar.gz")
+	cmd.Dir = steamcmdDir
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return "", fmt.Errorf("failed to extract steamcmd: %w — output: %s", err, string(out))
+	}
+
+	// Ensure the script is executable.
+	if err := os.Chmod(steamcmdPath, 0755); err != nil {
+		return "", fmt.Errorf("failed to chmod steamcmd.sh: %w", err)
+	}
+
+	// Verify the installation by running +quit (triggers first-time setup).
+	verify := exec.Command(steamcmdPath, "+quit")
+	verify.Dir = steamcmdDir
+	if out, err := verify.CombinedOutput(); err != nil {
+		return "", fmt.Errorf("steamcmd verification failed: %w — output: %s", err, string(out))
+	}
+
+	log.Printf("SteamCMD installed successfully at %s", steamcmdPath)
+	return steamcmdPath, nil
+}
+
+// RegisterService creates a systemd unit file for the Rust Dedicated Server
+// and enables it. If the caller does not have root access, the unit file is
+// written into installDir as a fallback so the user can install it manually.
+func RegisterService(installDir string, cfg DeployConfig) error {
+	serverPath := filepath.Join(installDir, "server", "RustDedicated")
+
+	unit := fmt.Sprintf(`[Unit]
+Description=Rust Dedicated Server (Corrosion Managed)
+After=network.target
+
+[Service]
+Type=simple
+User=root
+WorkingDirectory=%s/server
+ExecStart=%s -batchmode +server.hostname "%s" +server.port %d +rcon.port %d +rcon.password "%s" +rcon.web 1 +server.identity "corrosion" +server.maxplayers %d +server.worldsize %d +server.seed %d
+Restart=on-failure
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target
+`, installDir, serverPath, cfg.ServerName, cfg.ServerPort, cfg.RconPort,
+		cfg.RconPassword, cfg.MaxPlayers, cfg.WorldSize, cfg.Seed)
+
+	systemdPath := "/etc/systemd/system/rustserver.service"
+	if err := os.WriteFile(systemdPath, []byte(unit), 0644); err != nil {
+		// Fallback — write into installDir so the user can place it manually.
+		fallback := filepath.Join(installDir, "rustserver.service")
+		log.Printf("WARNING: cannot write to %s (%v), falling back to %s", systemdPath, err, fallback)
+		if writeErr := os.WriteFile(fallback, []byte(unit), 0644); writeErr != nil {
+			return fmt.Errorf("failed to write service file to fallback %s: %w", fallback, writeErr)
+		}
+	}
+
+	// Best-effort daemon-reload and enable — ignore errors (systemctl may not
+	// exist or the user may lack privileges).
+	_ = exec.Command("systemctl", "daemon-reload").Run()
+	_ = exec.Command("systemctl", "enable", "rustserver").Run()
+
+	log.Println("Systemd service registered for rustserver")
+	return nil
+}
+
+// downloadFile fetches url and writes the response body to dest on disk.
+func downloadFile(url, dest string) error {
+	resp, err := http.Get(url)
+	if err != nil {
+		return fmt.Errorf("GET %s failed: %w", url, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("GET %s returned status %d", url, resp.StatusCode)
+	}
+
+	out, err := os.Create(dest)
+	if err != nil {
+		return fmt.Errorf("failed to create file %s: %w", dest, err)
+	}
+	defer out.Close()
+
+	if _, err := io.Copy(out, resp.Body); err != nil {
+		return fmt.Errorf("failed to write to %s: %w", dest, err)
+	}
+
+	return nil
+}