fix: use cmd /c on Windows for shell command execution

The exec tool was hardcoded to use 'sh -c' which doesn't exist on Windows,
causing all tool calls to fail silently in gateway mode.

pkg/tools/shell.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 	"time"
 )
@@ -27,7 +28,7 @@ func NewExecTool(workingDir string, restrict bool) *ExecTool {
 		regexp.MustCompile(`\brmdir\s+/s\b`),
 		regexp.MustCompile(`\b(format|mkfs|diskpart)\b\s`), // Match disk wiping commands (must be followed by space/args)
 		regexp.MustCompile(`\bdd\s+if=`),
-		regexp.MustCompile(`>\s*/dev/sd[a-z]\b`),            // Block writes to disk devices (but allow /dev/null)
+		regexp.MustCompile(`>\s*/dev/sd[a-z]\b`), // Block writes to disk devices (but allow /dev/null)
 		regexp.MustCompile(`\b(shutdown|reboot|poweroff)\b`),
 		regexp.MustCompile(`:\(\)\s*\{.*\};\s*:`),
 	}
@@ -91,7 +92,12 @@ func (t *ExecTool) Execute(ctx context.Context, args map[string]interface{}) (st
 	cmdCtx, cancel := context.WithTimeout(ctx, t.timeout)
 	defer cancel()
 
-	cmd := exec.CommandContext(cmdCtx, "sh", "-c", command)
+	var cmd *exec.Cmd
+	if runtime.GOOS == "windows" {
+		cmd = exec.CommandContext(cmdCtx, "cmd", "/c", command)
+	} else {
+		cmd = exec.CommandContext(cmdCtx, "sh", "-c", command)
+	}
 	if cwd != "" {
 		cmd.Dir = cwd
 	}