Additively extend #982 build_forecast_overlay: class recommendation (§10.2,
strongest aggregate deficit per class), USP-from-deficits (§10.5, top-3),
degraded-honest commercial signal (§10.4, premise_kind=нежилое → available:False
+caveat when thin, never fabricates), and a §16 structural reason
(why/drivers/rejected/what_would_change/confidence/advisory) on every ranked
segment. §16 rejected-alternatives derived from the what_to_build ranking
runner-ups. Deterministic, no LLM, advisory, no new SQL. All #982 keys/behavior
preserved; schema extended additively (RecommendReason + optional fields).
31 new tests (86 total recommendation+velocity green).
