Assembly of the rolling plan view.

Returns past boards (up to 6 days), today's board, and intents for future days (up to 6 days). If no WeeklyPlan exists for the user, creates a trigger="pending" placeholder and enqueues a background generation — the response comes back immediately with plan_trigger="pending" so the client can poll until the real plan is ready. A second week view while pending does not re-enqueue: the placeholder short-circuits the current_plan is None check. The board build does, since the empty placeholder reads as lapsed there; the lock in evaluate_and_update_plan keeps the pair to one generation (#3027). The local plan lifecycle remains for athletes without a stored plan. Athletes with one read its mapped projection and never create a placeholder or tail roll.