fix(image): gracefully handle missing Docker/Podman engine

ImageUtils.hostInfo() now returns an empty string instead of throwing
RuntimeException when the container engine binary is missing (IOException)
or returns error output. This allows callers to fall back gracefully
rather than crashing when neither Docker nor Podman is installed.

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

Author: ruromero

src/main/java/io/github/guacsec/trustifyda/image/ImageUtils.java

@@ -281,10 +281,18 @@ static String hostInfo(String engine, String info) {
     var exec = Operations.getCustomPathOrElse(engine);
     var cmd = new String[] {exec, "info"};
 
-    var output = Operations.runProcessGetFullOutput(null, cmd, null);
+    Operations.ProcessExecOutput output;
+    try {
+      output = Operations.runProcessGetFullOutput(null, cmd, null);
+    } catch (RuntimeException e) {
+      if (e.getCause() instanceof IOException) {
+        return "";
+      }
+      throw e;
+    }
     if (output.getOutput().isEmpty()
         && (!output.getError().isEmpty() || output.getExitCode() != 0)) {
-      throw new RuntimeException(output.getError());
+      return "";
     }
 
     return output

src/test/java/io/github/guacsec/trustifyda/image/ImageUtilsTest.java

@@ -27,7 +27,6 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.AdditionalMatchers.aryEq;
 import static org.mockito.ArgumentMatchers.any;
@@ -549,9 +548,8 @@ void test_host_info_no_docker_path() {
                       isNull(), aryEq(new String[] {"docker", "info"}), isNull()))
           .thenReturn(output);
 
-      var exception =
-          assertThrows(RuntimeException.class, () -> ImageUtils.hostInfo("docker", "info"));
-      assertEquals("test-error", exception.getMessage());
+      var result = ImageUtils.hostInfo("docker", "info");
+      assertEquals("", result);
     }
   }