Initial MCM project: FastAPI + Textual TUI unified messenger

MultiCustomerMessenger supporting Telegram (python-telegram-bot),
WhatsApp (Green API) and SMS (python-gsmmodem-new). REST API with
Bearer-token auth, SQLAlchemy models for MariaDB, APScheduler for
background polling, and Textual TUI running in same asyncio event-loop.

db/database.py

@@ -0,0 +1,38 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, sessionmaker
+from sqlalchemy.pool import StaticPool
+from config import settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+_connect_args = {}
+_pool_class = None
+
+if settings.database_url.startswith("sqlite"):
+    _connect_args = {"check_same_thread": False}
+    _pool_class = StaticPool
+
+engine = create_engine(
+    settings.database_url,
+    connect_args=_connect_args,
+    **({"poolclass": _pool_class} if _pool_class else {}),
+    echo=settings.debug,
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+def init_db() -> None:
+    from db import models  # noqa: F401 – Modelle müssen importiert sein
+    Base.metadata.create_all(bind=engine)