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_passengers_load.sql

@@ -0,0 +1,82 @@
+-- Загрузка DDS dim_passengers: SCD1 UPSERT (UPDATE изменившихся + INSERT новых).
+
+-- Statement 1: UPDATE существующих записей (если атрибуты изменились).
+WITH src AS (
+    SELECT
+        d.passenger_id,
+        d.passenger_name
+    FROM (
+        SELECT
+            t.passenger_id,
+            t.passenger_name,
+            ROW_NUMBER() OVER (
+                PARTITION BY t.passenger_id
+                ORDER BY t.event_ts DESC NULLS LAST, t._load_ts DESC, t.ticket_no DESC
+            ) AS rn
+        FROM ods.tickets AS t
+        WHERE t.passenger_id IS NOT NULL
+            AND t.passenger_id <> ''
+            AND t.passenger_name IS NOT NULL
+            AND t.passenger_name <> ''
+    ) AS d
+    WHERE d.rn = 1
+)
+UPDATE dds.dim_passengers AS d
+SET passenger_name = s.passenger_name,
+    updated_at     = now(),
+    _load_id       = '{{ run_id }}',
+    _load_ts       = now()
+FROM src AS s
+WHERE d.passenger_bk = s.passenger_id
+    AND d.passenger_name IS DISTINCT FROM s.passenger_name;
+
+-- Statement 2: INSERT новых записей (MAX(sk) + ROW_NUMBER()).
+WITH src AS (
+    SELECT
+        d.passenger_id,
+        d.passenger_name
+    FROM (
+        SELECT
+            t.passenger_id,
+            t.passenger_name,
+            ROW_NUMBER() OVER (
+                PARTITION BY t.passenger_id
+                ORDER BY t.event_ts DESC NULLS LAST, t._load_ts DESC, t.ticket_no DESC
+            ) AS rn
+        FROM ods.tickets AS t
+        WHERE t.passenger_id IS NOT NULL
+            AND t.passenger_id <> ''
+            AND t.passenger_name IS NOT NULL
+            AND t.passenger_name <> ''
+    ) AS d
+    WHERE d.rn = 1
+),
+max_sk AS (
+    SELECT COALESCE(MAX(passenger_sk), 0) AS v
+    FROM dds.dim_passengers
+)
+INSERT INTO dds.dim_passengers (
+    passenger_sk,
+    passenger_bk,
+    passenger_name,
+    created_at,
+    updated_at,
+    _load_id,
+    _load_ts
+)
+SELECT
+    (SELECT v FROM max_sk) + ROW_NUMBER() OVER (ORDER BY s.passenger_id)::INTEGER,
+    s.passenger_id,
+    s.passenger_name,
+    now(),
+    now(),
+    '{{ run_id }}',
+    now()
+FROM src AS s
+WHERE NOT EXISTS (
+    SELECT 1
+    FROM dds.dim_passengers AS d
+    WHERE d.passenger_bk = s.passenger_id
+);
+
+ANALYZE dds.dim_passengers;