openai/gpt-chat-latest → A (9:1)

Side A removes the duplicate `server/src/html/forum.rs`, introduces `forum/mod.rs`, and moves the existing implementation into focused submodules (`feed.rs`, `views.rs`, `thread_morph.rs`, etc.), eliminating module-resolution ambiguity so `mod forum` has a single authoritative root. Side B mainly adds a detailed planning document plus a thin `RouteContext` wrapper and export, which lays groundwork but leaves most call sites unchanged and delivers little immediate functional value.