ANU-12: Bento Editor and Template Families

Status: Completion review passed; awaiting explicit ready-and-merge approval.

This change builds the production Anuva Bento editor boundary and coordinated template families on the completed ANU-11 contract and deterministic-player foundation.

• Linear issue ANU-12
• Implementation Plan
• Implementation Log
• Completion Report
• Normative editor and template documentation

The editor will author Main, Companion, and Emphasis as three independent surface documents in one presentation context. It will exchange validated, revision-aware messages with its host without owning CMS persistence.