Add third SQL query (bucket_rows) aggregating deals_total_count by
room_bucket ('студия','1','2','3','4+') across mapped competitors.
New fields:
- VelocityResult.by_room_bucket: aggregate {units, sqm, complexes_count}
- sample_competitors[].by_room_bucket: {bucket: units}
Bucket query wrapped в SAVEPOINT — failure degrades gracefully к empty
dict без abort outer tx.
CAST(:window_interval AS interval) pattern per PR #160 lesson.
Test coverage: 3 new tests (aggregation, empty fallback, sample entries).
Closes part of #161
SQLAlchemy text() parser confuses ':window_interval' (named param) followed
by '::interval' (cast operator) — exactly как было в PR #152 с :weights::jsonb.
Result: psycopg видит literal ':window_interval' в SQL → syntax error →
exception caught by velocity catch → return None → UI shows null.
## Fix
':window_interval::interval' → 'CAST(:window_interval AS interval)' (2 мест:
sales_rows query + _get_ekb_median percentile).
Pre-push code-reviewer должен был catch — добавим в feedback что для каждого
text() SQL grep ':[a-z]*::' before push.
Refs: PR #158 deploy verify, e2e velocity = null root cause
