Follow up to: #3576100 **Description:** AI Context now enforces subcontext integrity at the entity validation layer through `AiContextItemIntegrity` / `AiContextItemValidator`. This is the desired behavior for RC1, but the docs should explicitly describe the persistence contract. Document that: - A context item cannot be its own parent. - Subcontext hierarchies are limited to one level. - An item with children cannot become a subcontext itself. - `subcontext_type` is required when a parent is selected. - Parent deletion clears child `parent` and `subcontext_type` references. - These rules are enforced during entity validation, not only during selection. This is mostly documentation work, likely in developer docs plus a short note in the subcontext feature docs. **AI usage disclosures:** - [x] AI Assisted Issue - [x] AI Generated Code