feat(airflow): добавлен гейт целостности DDS для урока 4

- Зачем:
  - урок 4 должен показывать не только измерение сирот в DDS, но и остановку Airflow DAG при нарушении связи dds.event -> dds.click.
- Что:
  - добавлен assert_dds_integrity в etl_pipeline и документация управляемого красного сценария.
  - вынесены общие helper'ы для SQL-split и boolean-параметров Airflow.
  - добавлен урок 4 и обновлены навигация курса, план обучения и operations notes.
- Проверка:
  - python3 -m py_compile airflow/dags/etl_pipeline_dag.py airflow/dags/ddl_init_dag.py airflow/dags/kafka_load_dag.py airflow/dags/utils/airflow_params.py airflow/dags/utils/sql_helpers.py.
  - docker compose exec -T airflow-webserver airflow dags test etl_pipeline 2026-06-05T18:00:00 -c '{"full_refresh": true}'.

airflow/dags/utils/airflow_params.py

@@ -0,0 +1,33 @@
+"""Общие helper-функции для параметров Airflow DAG."""
+
+from __future__ import annotations
+
+TRUE_VALUES = {"1", "true", "t", "yes", "y", "on"}
+FALSE_VALUES = {"0", "false", "f", "no", "n", "off"}
+
+
+def _param_error(message: str) -> Exception:
+    try:
+        from airflow.exceptions import AirflowException
+
+        return AirflowException(message)
+    except ModuleNotFoundError:
+        return ValueError(message)
+
+
+def parse_bool_param(value: object, name: str) -> bool:
+    """Преобразует bool-параметр из dag_run.conf/params в явный boolean."""
+    if isinstance(value, bool):
+        return value
+
+    if isinstance(value, int) and value in (0, 1):
+        return bool(value)
+
+    if isinstance(value, str):
+        normalized = value.strip().lower()
+        if normalized in TRUE_VALUES:
+            return True
+        if normalized in FALSE_VALUES:
+            return False
+
+    raise _param_error(f"Параметр {name} должен быть boolean, получено: {value!r}")

airflow/dags/utils/sql_helpers.py

@@ -0,0 +1,153 @@
+"""Общие helper-функции для чтения SQL-файлов из Airflow DAG."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+
+def _sql_error(message: str) -> Exception:
+    try:
+        from airflow.exceptions import AirflowException
+
+        return AirflowException(message)
+    except ModuleNotFoundError:
+        return ValueError(message)
+
+
+def strip_sql_comments(sql_text: str) -> str:
+    """Удаляет SQL-комментарии, не трогая строки в кавычках."""
+    result: list[str] = []
+    i = 0
+    in_single_quote = False
+    in_double_quote = False
+
+    while i < len(sql_text):
+        char = sql_text[i]
+        next_char = sql_text[i + 1] if i + 1 < len(sql_text) else ""
+
+        if in_single_quote:
+            result.append(char)
+            if char == "'" and next_char == "'":
+                result.append(next_char)
+                i += 2
+                continue
+            if char == "'" and (i == 0 or sql_text[i - 1] != "\\"):
+                in_single_quote = False
+            i += 1
+            continue
+
+        if in_double_quote:
+            result.append(char)
+            if char == '"' and (i == 0 or sql_text[i - 1] != "\\"):
+                in_double_quote = False
+            i += 1
+            continue
+
+        if char == "'":
+            in_single_quote = True
+            result.append(char)
+            i += 1
+            continue
+
+        if char == '"':
+            in_double_quote = True
+            result.append(char)
+            i += 1
+            continue
+
+        if char == "-" and next_char == "-":
+            i += 2
+            while i < len(sql_text) and sql_text[i] not in "\r\n":
+                i += 1
+            continue
+
+        if char == "/" and next_char == "*":
+            i += 2
+            while (
+                i < len(sql_text) - 1
+                and not (sql_text[i] == "*" and sql_text[i + 1] == "/")
+            ):
+                if sql_text[i] in "\r\n":
+                    result.append(sql_text[i])
+                i += 1
+            i += 2
+            continue
+
+        result.append(char)
+        i += 1
+
+    return "".join(result)
+
+
+def split_sql_statements(sql_text: str) -> tuple[str, ...]:
+    """Делит SQL на команды по ';' вне строковых литералов."""
+    statements: list[str] = []
+    current: list[str] = []
+    cleaned_sql = strip_sql_comments(sql_text)
+    in_single_quote = False
+    in_double_quote = False
+    i = 0
+
+    while i < len(cleaned_sql):
+        char = cleaned_sql[i]
+        next_char = cleaned_sql[i + 1] if i + 1 < len(cleaned_sql) else ""
+
+        if in_single_quote:
+            current.append(char)
+            if char == "'" and next_char == "'":
+                current.append(next_char)
+                i += 2
+                continue
+            if char == "'" and (i == 0 or cleaned_sql[i - 1] != "\\"):
+                in_single_quote = False
+            i += 1
+            continue
+
+        if in_double_quote:
+            current.append(char)
+            if char == '"' and (i == 0 or cleaned_sql[i - 1] != "\\"):
+                in_double_quote = False
+            i += 1
+            continue
+
+        if char == "'":
+            in_single_quote = True
+            current.append(char)
+            i += 1
+            continue
+
+        if char == '"':
+            in_double_quote = True
+            current.append(char)
+            i += 1
+            continue
+
+        if char == ";":
+            statement = "".join(current).strip()
+            if statement:
+                statements.append(statement)
+            current = []
+            i += 1
+            continue
+
+        current.append(char)
+        i += 1
+
+    statement = "".join(current).strip()
+    if statement:
+        statements.append(statement)
+
+    return tuple(statements)
+
+
+def load_sql_statements(sql_root: Path, relative_path: str) -> tuple[str, ...]:
+    """Читает SQL-файл и возвращает отдельные команды."""
+    file_path = sql_root / relative_path
+    if not file_path.is_file():
+        raise _sql_error(f"SQL-файл не найден: {file_path}")
+
+    statements = split_sql_statements(file_path.read_text(encoding="utf-8"))
+    if not statements:
+        raise _sql_error(f"SQL-файл пустой: {file_path}")
+
+    return statements