dist: Address Copilot review suggestions from PR #1042 (GraalVM Community) (#1059)

- installer: surface a clear error when the GraalVM Community releases
  listing is not a JSON array, instead of silently treating an error
  payload (rate limit, auth failure, etc.) as "no releases" which later
  surfaced as a misleading "version not found" error.
- docs: fix the GraalVM Community advanced-usage example to check the
  installed binary versions (java/native-image --version) rather than
  running a non-existent HelloWorldApp classpath that fails when copied.
- tests: cover the new non-array release listing error path.

Rebuilt dist bundle.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/distributions/graalvm/installer.ts

@@ -391,7 +391,20 @@ export class GraalVMCommunityDistribution extends GraalVMDistribution {
         headers
       );
 
-      const releases = Array.isArray(response.result) ? response.result : [];
+      // A successful GitHub releases listing is always a JSON array (possibly
+      // empty). Anything else indicates an unexpected/error payload (rate
+      // limiting, auth failure, etc.) that must be surfaced instead of being
+      // silently treated as "no releases", which would later look like a
+      // misleading "version not found" error.
+      if (!Array.isArray(response.result)) {
+        throw new Error(
+          `Unexpected response while listing GraalVM Community releases from ${releasesUrl} ` +
+            `(HTTP status code: ${response.statusCode}). Expected a JSON array of releases. ` +
+            `Please check if the service is available at ${GRAALVM_COMMUNITY_DOWNLOAD_URL}.`
+        );
+      }
+
+      const releases = response.result;
       if (releases.length === 0) {
         break;
       }