feat: expand AI workflow support and refresh docs

docs/ai/ark-seedream-5-update.md

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+# Ark Seedream 5.0 Update
+
+This project now aligns its generic image-generation flow with the current Ark Seedream 5.0 usage pattern.
+
+## What changed
+
+- Single-image text-to-image is supported through the generic design-image endpoint.
+- Reference-image generation is supported by passing the latest uploaded chat image into the image model.
+- Multi-image generation is supported with Ark sequential image generation.
+- When the requested image count is greater than 1, the backend collects stream events and returns a final image list to the chat UI.
+
+## Runtime mapping
+
+- Backend image model entry:
+  - `Server/app/api/v1/ai_llm.py`
+  - Uses `client.images.generate(...)`
+  - Supports:
+    - `sequential_image_generation="disabled"` for single image
+    - `sequential_image_generation="auto"` for multi-image
+    - `SequentialImageGenerationOptions(max_images=...)`
+
+- Generic API endpoint:
+  - `POST /ai/generate-design-images`
+  - File: `Server/app/api/v1/ai_pattern.py`
+
+- Chat tool:
+  - `generate_design_images`
+  - File: `Server/app/api/v1/ai_tools.py`
+
+- Frontend executor:
+  - `Designer/src/utils/aiToolExecutor.ts`
+
+## Supported use cases
+
+- "生成一张高级感海报背景图"
+- "根据这张参考图出 4 张不同方向稿"
+- "生成一组连贯插画"
+- "做 3 张 KV 草案给我选"
+
+## Notes
+
+- The current chat UI renders the returned image URLs directly inside the assistant conversation.
+- The current implementation caps multi-image generation at 4 images per request.
+- The project still uses the configured `AI_IMAGE_EDIT_MODEL` as the unified Ark image-generation model slot.