[app] fix app share URI construction

and introduce 'packages' suffix that gets appended to the base URI

app/src/main/java/org/fdroid/fdroid/data/App.java

@@ -350,7 +350,8 @@ public class App implements Comparable<App>, Parcelable {
         Repository repo = FDroidApp.getRepoManager(context).getRepository(repoId);
         if (repo == null || repo.getWebBaseUrl() == null) return null;
         return Uri.parse(repo.getWebBaseUrl()).buildUpon()
-                .path(packageName)
+                .appendPath("packages")
+                .appendPath(packageName)
                 .build();
     }