feat(tradein): blend Avito IMV anchor into estimate + ДКП corridor advisory — backend (#651, #652)
Radius-median underestimated premium/view units ~2x. #651: blend real Avito
IMV (house_imv_evaluations per house_id) one-directional raise-only — when
IMV recommended > median*1.15, median = blend(median,IMV,w=0.5), range_high
extends to IMV higher. #652: ДКП corridor (rosreestr deals, RUB/m2, advisory
+ soft +-25% note, no clamp). Behind config flags (default on), null-guarded
no-op when absent. Adds avito_imv + dkp_corridor to AggregatedEstimate.
Validated on live DB (B. Yeltsina 6 80m2: 19.7M->25.8M, range->33.5M).
Frontend surfacing (tradein-mvp/frontend) follows in next commit.
70ee7b282c