Fix DiT initialization: pass model name only, not full path

src/ace_step_engine.py

@@ -110,9 +110,11 @@ class ACEStepEngine:
             logger.info(f"Initializing DiT handler with model: {dit_model_path}")
             
             # Initialize DiT handler (handles main diffusion model, VAE, text encoder)
+            # Note: handler auto-detects checkpoints dir as project_root/checkpoints
+            # config_path should be just the model name, not full path
             status_dit, success_dit = self.dit_handler.initialize_service(
                 project_root=project_root,
-                config_path=str(checkpoints_dir / dit_model_path),
+                config_path=dit_model_path,  # Just model name, handler adds checkpoints/
                 device="auto",
                 use_flash_attention=False,
                 compile_model=False,