feat(dds): реализован слой dds для bookings

- Зачем:
  - подготовлен учебный Star Schema слой для перехода от ODS к аналитике и витринам.
- Что:
  - добавлены 21 SQL-файл для DDS (DDL/LOAD/DQ) с SCD1/SCD2 и фактом `fact_flight_sales`.
  - добавлены DAG `bookings_dds_ddl` и `bookings_to_gp_dds`, а также smoke-тесты структуры DAG.
  - обновлены `sql/ddl_gp.sql` и документация (`README`, `docs/*`, `db_schema`) под поток `stg -> ods -> dds`.
- Проверка:
  - make test.

sql/dds/dim_airplanes_load.sql

@@ -0,0 +1,92 @@
+-- Загрузка DDS dim_airplanes: SCD1 UPSERT (UPDATE изменившихся + INSERT новых).
+
+-- Statement 1: UPDATE существующих записей (если атрибуты изменились).
+WITH seats_agg AS (
+    SELECT
+        s.airplane_code,
+        COUNT(*)::INTEGER AS total_seats
+    FROM ods.seats AS s
+    GROUP BY s.airplane_code
+),
+src AS (
+    SELECT
+        a.airplane_code,
+        a.model,
+        a.range_km,
+        a.speed_kmh,
+        COALESCE(sa.total_seats, 0) AS total_seats
+    FROM ods.airplanes AS a
+    LEFT JOIN seats_agg AS sa
+        ON sa.airplane_code = a.airplane_code
+)
+UPDATE dds.dim_airplanes AS d
+SET model       = s.model,
+    range_km    = s.range_km,
+    speed_kmh   = s.speed_kmh,
+    total_seats = s.total_seats,
+    updated_at  = now(),
+    _load_id    = '{{ run_id }}',
+    _load_ts    = now()
+FROM src AS s
+WHERE d.airplane_bk = s.airplane_code
+    AND (
+        d.model IS DISTINCT FROM s.model
+        OR d.range_km IS DISTINCT FROM s.range_km
+        OR d.speed_kmh IS DISTINCT FROM s.speed_kmh
+        OR d.total_seats IS DISTINCT FROM s.total_seats
+    );
+
+-- Statement 2: INSERT новых записей (MAX(sk) + ROW_NUMBER()).
+WITH seats_agg AS (
+    SELECT
+        s.airplane_code,
+        COUNT(*)::INTEGER AS total_seats
+    FROM ods.seats AS s
+    GROUP BY s.airplane_code
+),
+src AS (
+    SELECT
+        a.airplane_code,
+        a.model,
+        a.range_km,
+        a.speed_kmh,
+        COALESCE(sa.total_seats, 0) AS total_seats
+    FROM ods.airplanes AS a
+    LEFT JOIN seats_agg AS sa
+        ON sa.airplane_code = a.airplane_code
+),
+max_sk AS (
+    SELECT COALESCE(MAX(airplane_sk), 0) AS v
+    FROM dds.dim_airplanes
+)
+INSERT INTO dds.dim_airplanes (
+    airplane_sk,
+    airplane_bk,
+    model,
+    range_km,
+    speed_kmh,
+    total_seats,
+    created_at,
+    updated_at,
+    _load_id,
+    _load_ts
+)
+SELECT
+    (SELECT v FROM max_sk) + ROW_NUMBER() OVER (ORDER BY s.airplane_code)::INTEGER,
+    s.airplane_code,
+    s.model,
+    s.range_km,
+    s.speed_kmh,
+    s.total_seats,
+    now(),
+    now(),
+    '{{ run_id }}',
+    now()
+FROM src AS s
+WHERE NOT EXISTS (
+    SELECT 1
+    FROM dds.dim_airplanes AS d
+    WHERE d.airplane_bk = s.airplane_code
+);
+
+ANALYZE dds.dim_airplanes;