fix: default client fileApi is the Nexus raw tdlm-client; tell the player when the manifest cannot be fetched

The default pointed at packages.dandanton.com/tdlm-client/latest (404), so the first-launch auto install
silently did nothing. It now points at https://maven.dandanton.com/repository/tdlm-client, and a failed or
malformed manifest shows an error and opens the import wizard (same behaviour as the Start menu install).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

HMCL/src/main/java/org/jackhuang/hmcl/Metadata.java

@@ -141,9 +141,9 @@ public final class Metadata {
         return null;
     }
 
-    /// Default client Server Modpack fileApi (CDN mirror of Pack's `tdlm-client/latest` layout).
+    /// Default client Server Modpack fileApi: the Nexus raw repository `tdlm-client` read through the CDN host.
     public static final String DEFAULT_CLIENT_FILE_API =
-            "https://packages.dandanton.com/tdlm-client/latest";
+            "https://maven.dandanton.com/repository/tdlm-client";
 
     /// Stable client update root (`server-manifest.json` and `overrides/` live under this URL).
     ///

HMCL/src/main/java/org/jackhuang/hmcl/ui/Controllers.java

@@ -398,12 +398,22 @@ public final class Controllers {
                         .whenComplete(Schedulers.javafx(), (result, exception) -> {
                             if (exception != null) {
                                 LOG.warning("Failed to fetch client Server Modpack manifest", exception);
+                                Controllers.dialog(
+                                        manifestUrl + "\n" + exception.getMessage(),
+                                        i18n("message.error"),
+                                        MessageType.ERROR);
+                                Instances.importModpack();
                                 return;
                             }
                             ServerModpackManifest manifest =
                                     JsonUtils.fromMaybeMalformedJson(result, ServerModpackManifest.class);
                             if (manifest == null) {
                                 LOG.warning("Malformed client Server Modpack manifest from " + manifestUrl);
+                                Controllers.dialog(
+                                        i18n("modpack.type.server.malformed"),
+                                        i18n("message.error"),
+                                        MessageType.ERROR);
+                                Instances.importModpack();
                                 return;
                             }
                             Controllers.getDecorator().startWizard(