feat: add knowledge-grounded search suggestions

[lgqfhwy]

What changed

• add enable_suggestion support to the AI shopping /api/chat_search flow
• generate three knowledge-grounded product-search suggestions concurrently with the reply after the final product snapshot is fixed
• return suggestion failures in a nested payload without affecting the main streamed reply
• add standalone POST /api/search_suggestion, which accepts a query, performs knowledge retrieval, and returns one suggestion
• extract shared knowledge evidence handling and add a shared, config-driven suggestion generator, tool schema, context builder, and validator
• add a knowledge-only HA3 recall type for standalone deployments without AIChatConfig or Ha3ChatRecallConf

[github-actions]

Code review by ChatGPT

[github-actions]

Code review by ChatGPT