openai/gpt-chat-latest → B (8:1)

Commit B makes a substantially larger contribution. It introduces a new `RouteContext` abstraction with a dedicated routing module, exports it for use across the HTML layer, and adds a detailed engineering plan documenting the intended `ItemId`/routing refactor, migration phases, risks, and testing strategy. While much of the added content is documentation, it also includes reusable code that establishes a new API for route generation. Commit A is a small cleanup that removes a UI preview section from a template, which is a much narrower change with limited architectural impact.