refactor(sql): reorganize sql files into structured directory hierarchy

Move DDL files from flat ddl/ directory to sql/ddl/ with layer-based
subdirectories (stg, ods, dds, dm). Move batch transformation SQL from
jobs/ to sql/ layer directories. Update scripts and documentation to
reflect new paths for improved organization and Airflow integration.

sql/ddl/00_databases.sql

@@ -0,0 +1,13 @@
+-- ============================================================================
+-- Создание баз данных для слоёв хранилища
+-- ============================================================================
+-- stg — Staging: сырые данные из Kafka
+-- ods — Operational Data Store: типизированные данные с DQ
+-- dds — Detailed Data Store: детальные сущности для аналитики
+-- dm  — Data Marts: витрины для BI
+-- ============================================================================
+
+CREATE DATABASE IF NOT EXISTS stg;
+CREATE DATABASE IF NOT EXISTS ods;
+CREATE DATABASE IF NOT EXISTS dds;
+CREATE DATABASE IF NOT EXISTS dm;