refactor(airflow): move DAGs to airflow/dags and update paths

- Why:
  - keep Airflow artifacts under a single airflow/ directory
  - align repository layout with intended project structure
- What:
  - move dags/ to airflow/dags/ and update compose mounts
  - make SQL root resolution work in container and local runs
  - update DAG path references in README, AGENTS, ARCHITECTURE, and plans
  - remove tracked Python cache artifacts from old DAG location
- Check:
  - airflow dags list
  - airflow dags list-import-errors
  - e2e success: ddl_init, kafka_load(limit=50), etl_pipeline

README.md

@@ -115,7 +115,6 @@ flowchart LR
 
 ```
 .
-├── dags/             # Airflow DAGs для оркестрации
 ├── sql/
 │   ├── ddl/          # DDL по слоям
 │   │   ├── 00_databases.sql
@@ -128,6 +127,7 @@ flowchart LR
 │   └── dm/           # Batch SQL: DDS -> DM
 ├── scripts/          # Служебные shell-скрипты (legacy fallback, не основной путь)
 ├── airflow/          # Конфигурация Airflow
+│   ├── dags/         # Airflow DAGs для оркестрации
 │   └── requirements.txt
 ├── docs/             # Документация
 │   └── ARCHITECTURE.md   # Подробное описание слоёв