fix(site-finder): narrow except clauses, fix quarter fallback WKT, add LIMIT to zouit query

Addresses review-bot blockers on PR #190 (4 reviews flagged same issues):

1. Narrow except in quarter_dump_lookup.py:
   - line 579/651: except Exception -> (OperationalError, ProgrammingError) для outer DB queries
   - line 598/668: except Exception -> (ValueError, json.JSONDecodeError) для json.loads fallback

2. _get_parcel_wkt fallback (line 506-521): cad_quarters_geom хранит 3-segment quarter keys,
   а cad_num передавался 4-segment -> fallback всегда возвращал NULL. Теперь derive_quarter_cad(cad_num).

3. _get_zouit_engineering_overlaps: добавлен LIMIT 100 для unbounded jsonb_array_elements fan-out
   (engineering_structures query уже имел LIMIT 50).

backend/app/services/site_finder/quarter_dump_lookup.py

@@ -19,6 +19,7 @@ from datetime import UTC, datetime, timedelta
 from typing import Any
 
 from sqlalchemy import text
+from sqlalchemy.exc import OperationalError, ProgrammingError
 from sqlalchemy.orm import Session
 
 logger = logging.getLogger(__name__)
@@ -505,7 +506,9 @@ def _get_parcel_wkt(db: Session, cad_num: str) -> str | None:
     if row is not None and row[0] is not None:
         return str(row[0])
 
-    # Fallback: кварталы (более крупный объект — менее точно, но лучше чем ничего)
+    # Fallback: кварталы (более крупный объект — менее точно, но лучше чем ничего).
+    # cad_quarters_geom хранит 3-сегментные ключи (66:41:0204016), не 4-сегментные.
+    quarter_key = derive_quarter_cad(cad_num)
     row = db.execute(
         text(
             """
@@ -515,7 +518,7 @@ def _get_parcel_wkt(db: Session, cad_num: str) -> str | None:
              LIMIT 1
             """
         ),
-        {"c": cad_num},
+        {"c": quarter_key},
     ).first()
     if row is not None and row[0] is not None:
         return str(row[0])
@@ -573,7 +576,7 @@ def _get_engineering_structures_by_boundary(
             ),
             {"q": quarter, "wkt": parcel_wkt, "radius_m": radius_m},
         ).fetchall()
-    except Exception as e:
+    except (OperationalError, ProgrammingError) as e:
         logger.warning(
             "engineering_structures query failed for quarter=%s: %s",
             quarter,
@@ -592,7 +595,7 @@ def _get_engineering_structures_by_boundary(
         if geom_raw:
             try:
                 geom_dict = json.loads(geom_raw)
-            except Exception:
+            except (ValueError, json.JSONDecodeError):
                 geom_dict = {}
 
         result.append(
@@ -641,11 +644,12 @@ def _get_zouit_engineering_overlaps(
                        ),
                        ST_GeomFromText(:wkt, 4326)
                    )
+                 LIMIT 100
                 """
             ),
             {"q": quarter, "wkt": parcel_wkt},
         ).fetchall()
-    except Exception as e:
+    except (OperationalError, ProgrammingError) as e:
         logger.warning(
             "zouit_engineering query failed for quarter=%s: %s",
             quarter,
@@ -662,7 +666,7 @@ def _get_zouit_engineering_overlaps(
         if geom_raw:
             try:
                 geom_dict = json.loads(geom_raw)
-            except Exception:
+            except (ValueError, json.JSONDecodeError):
                 geom_dict = {}
 
         subcategory_raw = props.get("subcategory")