Add Flux2KleinPipeline model_index.json and register in manifest

manifest.json

@@ -1,6 +1,6 @@
 {
   "model_version": "binary g128 (Apple Silicon mlx-1bit deployment)",
-  "total_bytes": 3428210775,
+  "total_bytes": 3428210856,
   "files": [
     {
       "remote_path": "LICENSE",
@@ -17,6 +17,11 @@
       "size": 11996,
       "sha256": "1527258bbdd58161a3241245985c78ad5503635fd32bc2d0d37634c192a574e5"
     },
+    {
+      "remote_path": "model_index.json",
+      "size": 81,
+      "sha256": "ecb4735e37691a8733f62957fd6c548f841af40624905bb24fa639756153c8a1"
+    },
     {
       "remote_path": "scheduler/scheduler_config.json",
       "size": 486,

model_index.json

@@ -0,0 +1,4 @@
+{
+  "_class_name": "Flux2KleinPipeline",
+  "_diffusers_version": "0.37.0.dev0"
+}