~anthropic/claude-sonnet-latest → B (6:4)

Side A is a pure mechanical split/reorganization of forum.rs into submodules with no behavior change (net-zero functional value, mostly file-move churn). Side B implements a real UX/architecture improvement: it removes redirect-based auth flow in favor of AJAX form morphing, adds error/success fragment rendering, updates the shared poem JS to handle in-place form updates, and adds corresponding CSS — a genuine functional feature with lasting design impact.