Switch run_yandex_city_sweep from iterating 5 geographic anchors x 2 shallow
pages to a single EKB center anchor (56.8400, 60.6050) with exhaustive
rooms x price-range combos (5 room types x 6 price buckets = 30 combos),
radius_m=25000 to cover the whole city.
- scrape_pipeline.py: new params rooms_list/price_ranges; anchors=None (prod)
always uses EKB center; fetch_around_multi_room called in combos mode
- 119_yandex_city_sweep_center_combos.sql: updates default_params
(radius_m: 1500 -> 25000, pages_per_anchor: 2 -> 3)
- tests: 2 new tests assert center coords + combos wiring (prod mode and
explicit-anchors backward-compat); 1836 suite green
