SQL migration 064: adds houses.imv_status + last_imv_attempt_at + imv_error_reason
columns, creates house_imv_evaluations (1:1 with houses, latest IMV result)
and house_suggestions (8 Avito similar lots per house, UNIQUE on (house_id, ext_item_id)).
Script scripts/backfill-house-imv.py: resumable iterator that picks houses with
imv_status='pending' AND lat/lon NOT NULL, runs evaluate_via_imv() per house with
median lot-params from linked listings, saves house_imv_evaluations +
house_placement_history (from result.placement_history items) + house_suggestions
(from result.suggestions items). Configurable --batch, --delay, --limit-total.
Survives restart via imv_status state machine ('pending' -> 'ok'/'not_found'/
'transient_error'/'error'/'no_params'/'no_address'). Long backoff on
IMVAuthError (anti-captcha).
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