## Summary
- Added Go API route `PUT /api/v1/chats/:chat_id` to align with Python
`PUT /api/v1/chats/<chat_id>` chat update behavior.
- Added Go API route `PATCH /api/v1/chats/:chat_id` to align with Python
`PATCH /api/v1/chats/<chat_id>` partial chat update behavior.
- Added matching handler and service logic for owner checks, tenant
validation, persisted-field filtering, read-only field filtering,
`dataset_ids` to `kb_ids` conversion, and PATCH shallow merge semantics
for `prompt_config` and `llm_setting`.
