feat: Add user-provided entities support to retain endpoint

[phamgialinhlx]

Summary

• Add support for user-provided entities in the retain endpoint that get merged with auto-extracted entities
• Entities can be passed with each memory item as [{"text": "...", "type": "..."}]
• User entities are deduplicated (case-insensitive) against LLM-extracted entities before merging

Changes

• API: Added EntityInput model and entities field to MemoryItem
• Engine: Updated entity processing to merge user entities with extracted ones
• Clients: Updated Python, TypeScript, and control plane clients with entity support

[nicoloboschi]

Thanks for your contribution!

Could you elaborate on the use case of this feature?
While I understand how it works, its important that is clear why and when to use it

[phamgialinhlx]

Thanks for your contribution!

Could you elaborate on the use case of this feature? While I understand how it works, its important that is clear why and when to use it

In some cases I already know which entities are in the chunks and want to make sure they get included. For example, critical entities like key product names that I've already extracted using regex - I want to pass those directly rather than hoping the LLM picks them up