fix: load comfy_extras nodes even when server.py import fails

server.py cannot load due to a ComfyUI internal module shadowing bug
(comfy/utils.py file shadows utils/ package). Decouple init_extra_nodes()
from server.py loading so NODE_CLASS_MAPPINGS still gets populated from
comfy_extras (UpscaleModelLoader, etc.) even without full PromptServer setup.

Also fix app.py to re-read from cached sys.modules[nodes] after
import_custom_nodes() instead of using stale initial copy.

Fixes the upscale-model-loader runtime e2e test.

comfyui_to_python/node_runtime.py

@@ -261,7 +261,14 @@ def import_custom_nodes() -> None:
     server_mod = _load_module("server", os.path.join(comfyui_path, "server.py"))
 
     if execution_mod is None or server_mod is None:
-        log.debug("import_custom_nodes: could not load required modules")
+        log.debug(
+            "import_custom_nodes: could not load execution/server modules. "
+            "Proceeding without full PromptServer/PromptQueue setup."
+        )
+        # Even without server, we can still populate NODE_CLASS_MAPPINGS from
+        # comfy_extras and built-in extra nodes.
+        if nodes_mod is not None and hasattr(nodes_mod, "init_extra_nodes"):
+            asyncio.run(nodes_mod.init_extra_nodes())
         return
 
     loop = asyncio.new_event_loop()