fix(site-finder): db.rollback() в velocity catches + SAVEPOINT zoning/success_rec

velocity.py 3 internal try/except возвращали None БЕЗ db.rollback(). PR #154
SAVEPOINT не помог — exception не propagates из velocity. Postgres tx
aborted внутри, cascade InFailedSqlTransaction на следующих queries.

Fix:
- velocity.py: db.rollback() в 3 catch блоках
- parcels.py: SAVEPOINT обёртки для zoning + success_recommendation

Refs: user reports 2026-05-15 cascade 500

backend/app/api/v1/parcels.py

@@ -1658,6 +1658,7 @@ def analyze_parcel(
         "lon": centroid_lon,
     }
     try:
+        with db.begin_nested():
             zoning_row = (
                 db.execute(
                     text("""
@@ -1692,6 +1693,7 @@ def analyze_parcel(
     success_recommendation: dict[str, Any] | None = None
     if district_row:
         try:
+            with db.begin_nested():
                 success_rows = (
                     db.execute(
                         text("""

backend/app/services/site_finder/velocity.py

@@ -126,6 +126,13 @@ def compute_velocity(
         )
     except Exception:
         logger.exception("velocity: competitor query failed for wkt=%s", parcel_geom_wkt[:80])
+        # КРИТИЧНО: rollback aborted transaction чтобы caller (analyze_parcel)
+        # мог продолжить выполнять последующие queries. Иначе caller получает
+        # cascade InFailedSqlTransaction на следующей SQL execute.
+        try:
+            db.rollback()
+        except Exception:
+            pass
         return None
 
     if not comp_rows:
@@ -186,6 +193,11 @@ def compute_velocity(
         )
     except Exception:
         logger.exception("velocity: sale_graph query failed for obj_ids=%s", obj_ids[:5])
+        # КРИТИЧНО: rollback aborted transaction (см. competitor query комментарий)
+        try:
+            db.rollback()
+        except Exception:
+            pass
         return None
 
     if not sales_rows:
@@ -311,6 +323,11 @@ def _get_ekb_median(db: Session, months_window: int = 6) -> float | None:
         )
     except Exception:
         logger.warning("velocity: ekb_median query failed, using fallback")
+        # КРИТИЧНО: rollback aborted transaction
+        try:
+            db.rollback()
+        except Exception:
+            pass
         return None
 
     if row and row["median"] is not None: