fix: include stderr in Gradle init script failure warning

Log the error output alongside the exit code when gradle daListProjects
fails, so the root cause is visible without rerunning manually.

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

Author: Strum355

src/main/java/io/github/guacsec/trustifyda/impl/ExhortApi.java

@@ -1002,7 +1002,11 @@ private List<Path> discoverGradleSubprojects(Path workspaceDir, Set<String> igno
               null);
 
       if (output.getExitCode() != 0) {
-        LOG.warning("gradle daListProjects failed with exit code " + output.getExitCode());
+        LOG.warning(
+            "gradle daListProjects failed with exit code "
+                + output.getExitCode()
+                + ": "
+                + output.getErrorOutput());
         return WorkspaceUtils.filterByIgnorePatterns(workspaceDir, manifestPaths, ignorePatterns);
       }