The legacy resolve_cian_zhk_url hit /zhk/<id>/ which now 404s, leaving the
318 geo-matched cian houses (house_sources.ext_id set, cian_zhk_url NULL)
unfetchable -> the newbuilding-enrichment backfill matched 0 houses.
Add resolve_cian_zhk_url_via_search(nb_id): fetch the cat.php newbuilding SERP
and extract the canonical zhk-<slug>.cian.ru url, ANCHORED on the
<h1 data-name="Title"> header anchor (NOT naive first-match — the SERP carries
promo/recommendation zhk-* links before the title that would otherwise resolve
the wrong ЖК and silently corrupt enrichment). Validated against the real
2.81MB prod SERP + an adversarial poisoned-recommendation test.
Wire into newbuilding_enrich_backfill: broaden selection to "has ext_id OR
cian_zhk_url", resolve+persist the url under a SAVEPOINT before enriching,
rate-limited + resumable + idempotent. Keep the old resolver (deprecated).
Bounded prod proof (5 houses, direct): 5/5 urls resolved+persisted, 3/5 fully
enriched (+18 price_dynamics, +3 reliability); the 2 misses were direct-mode
anti-bot on the 2nd fetch. Full 318-run gated on the cian mobile proxy
(mproxy.site) being restored. code-reviewer APPROVE (SQL/idempotency) +
resolver hardened against wrong-ЖК. 19 tests green.
Refs #972.
