Agentic demo improvements - NPU and Qwen3Coder (#3790)

### 🛠 Summary

[CVS-173251](https://jira.devtools.intel.com/browse/CVS-173251)
Adding NPU models and usecases to the demo 
Adding Qwen3Coder export and usage.

### 🧪 Checklist

- [ ] Unit tests added.
- [ ] The documentation updated.
- [ ] Change follows security best practices.
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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: przepeck

demos/common/export_models/export_model.py

@@ -398,8 +398,8 @@ def export_text_generation_model(model_repository_path, source_model, model_name
         print("Exporting LLM model to ", llm_model_path)
         if not os.path.isdir(llm_model_path) or args['overwrite_models']:
             if task_parameters['target_device'] == 'NPU':
-                if precision != 'int4':
-                    print("NPU target device requires int4 precision. Changing to int4")
+                if precision != 'int4' and precision != 'nf4':
+                    print("NPU target device requires int4 or nf4 precision. Changing to int4")
                     precision = 'int4'
                 if task_parameters['extra_quantization_params'] == "":
                     print("Using default quantization parameters for NPU: --sym --ratio 1.0 --group-size -1")