feat(sf-18): add v_domrf_objects_with_sales view with is_sales_started flag

View derives is_sales_started (bool) via EXISTS subquery on domrf_kn_flats.
Enables SiteFinder to separate pre-sale buildings (no flats listed yet) from
active-sale ones. 75/1322 Строящиеся buildings in region 66 are pre-sale (5.7%).

data/sql/105_add_sales_started_flag.sql

@@ -0,0 +1,44 @@
+-- 105_add_sales_started_flag.sql
+--
+-- Context: SF FixList #18 (Wave 3)
+-- Purpose: Expose is_sales_started flag on domrf_kn_objects so SiteFinder can
+--          distinguish "Строящиеся с открытыми продажами" from pre-sale buildings
+--          (those where domrf_kn_flats has no rows for that obj_id yet).
+--
+-- Design decision: VIEW instead of GENERATED ALWAYS AS column.
+--   - PostgreSQL GENERATED columns do not support subqueries (only immutable expressions).
+--   - A VIEW is idempotent (CREATE OR REPLACE), needs no backfill, and stays fresh.
+--   - Consumers query v_domrf_objects_with_sales in place of domrf_kn_objects where
+--     the flag is needed; the base table remains unchanged for scrapers / ON CONFLICT.
+--
+-- Audit (2026-05-17, region_cd=66, site_status='Строящиеся'):
+--   total_buildings: 1322
+--   with_flats (is_sales_started=TRUE):  1247  (94.3%)
+--   without_flats (pre-sale / no flats):   75  ( 5.7%)
+--
+-- Dependencies: domrf_kn_objects, domrf_kn_flats
+-- Deploy order: standalone, no existing deps to drop first
+-- Idempotent: yes (CREATE OR REPLACE VIEW)
+
+BEGIN;
+
+CREATE OR REPLACE VIEW v_domrf_objects_with_sales AS
+SELECT
+    o.*,
+    EXISTS (
+        SELECT 1
+        FROM domrf_kn_flats f
+        WHERE f.obj_id = o.obj_id
+    ) AS is_sales_started
+FROM domrf_kn_objects o;
+
+COMMENT ON VIEW v_domrf_objects_with_sales IS
+    'domrf_kn_objects + is_sales_started (bool). '
+    'TRUE когда в domrf_kn_flats есть хотя бы одна запись для данного obj_id. '
+    'Позволяет отличать строящиеся дома с открытыми продажами от pre-sale объектов.';
+
+COMMENT ON COLUMN v_domrf_objects_with_sales.is_sales_started IS
+    'Derived: TRUE если EXISTS (SELECT 1 FROM domrf_kn_flats WHERE obj_id = o.obj_id). '
+    'Pre-sale = FALSE (квартиры ещё не выложены на domrf.ru).';
+
+COMMIT;