docs(FR-2543): update model serving documentation with new features (#6611)

Resolves #6687 (FR-2543)

## Summary

- Rewrite and expand the Model Serving documentation with comprehensive coverage of new features
- Document the **Model Store** tab for browsing, filtering, and importing pre-configured models
- Document the **Inference Runtime Variant** options (vLLM, NVIDIA NIM, Hugging Face TGI, SGLang, etc.) with runtime-specific parameter tabs
- Document the **Custom (Default)** runtime mode with **Enter Command** and **Use Config File** sub-modes
- Document the **Replicas & Resources** section and **Advanced Settings**
- Document **admin-only** features: Model Store Management tab, model card creation/editing, and the "Create Service from Model" workflow
- Add screenshots for all new sections (English UI) across all 4 languages

## Changes

- `model_serving/model_serving.md` (en/ko/ja/th): full rewrite with new sections
- `*/images/`: 11 new/updated screenshots (service_launcher1, service_launcher_runtime_variant, service_launcher_command_mode, service_launcher2, service_launcher_runtime_params, service_launcher3, serving_list_page, model_store_page, admin_serving_page, admin_model_card_list, admin_model_card_modal, model_card_detail_modal, model_clone_dialog)

## Test plan

- [ ] Verify Inference Runtime Variant dropdown options match the current UI
- [ ] Verify Enter Command / Use Config File mode descriptions are accurate
- [ ] Verify admin Model Store Management tab content is accurate
- [ ] Verify all screenshots show English UI labels

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Author: nowgnuesLee