feat(airflow): configure ClickHouse connection and update infrastructure

Update Airflow configuration to integrate with ClickHouse DWH instead of
PostgreSQL training database. Changes include:

- Switch Airflow dependencies from PostgreSQL to ClickHouse connector
- Update docker-compose to use ClickHouse connection and correct Dockerfile
- Refactor airflow/requirements.txt to include only essential packages
- Add DAGs directory for ETL pipeline orchestration
- Update documentation to reflect Airflow integration and access credentials
- Adjust service dependencies to wait for ClickHouse startup

docs/ARCHITECTURE.md

@@ -586,9 +586,11 @@ INSERT INTO dm.daily_traffic SELECT * FROM dm.v_daily_traffic;
 
 ### Airflow-оркестрация
 
+Инфраструктура Airflow развёрнута и готова к использованию:
+
 ```python
-# dag.py
-with DAG('clickhouse_etl'):
+# dags/etl_pipeline_dag.py
+with DAG('etl_pipeline'):
     ddl = BashOperator(task_id='ddl', bash_command='make ddl')
     load = BashOperator(task_id='load', bash_command='make data')
     transform = BashOperator(task_id='transform', bash_command='make transform')
@@ -596,6 +598,11 @@ with DAG('clickhouse_etl'):
     ddl >> load >> transform
 ```
 
+**Подключение к ClickHouse:**
+- Connection: `clickhouse_default`
+- URL: `clickhouse://default:123456@clickhouse:8123/default`
+- Provider: `clickhouse-connect` (в `airflow/requirements.txt`)
+
 ---
 
 ## Полезные запросы