Refactor project structure and enhance Docker configuration

- Updated `.dockerignore` to exclude test and development artifacts, optimizing the Docker image size.
- Refactored `main.py` to delegate execution to `duty_teller.run.main()`, simplifying the entry point.
- Introduced a new `duty_teller` package to encapsulate core functionality, improving modularity and organization.
- Enhanced `pyproject.toml` to define a script for running the application, streamlining the execution process.
- Updated README documentation to reflect changes in project structure and usage instructions.
- Improved Alembic environment configuration to utilize the new package structure for database migrations.

duty_teller/db/__init__.py

@@ -0,0 +1,52 @@
+"""Database layer: SQLAlchemy models, Pydantic schemas, repository, init."""
+
+from duty_teller.db.models import Base, User, Duty
+from duty_teller.db.schemas import (
+    UserCreate,
+    UserInDb,
+    DutyCreate,
+    DutyInDb,
+    DutyWithUser,
+)
+from duty_teller.db.session import (
+    get_engine,
+    get_session_factory,
+    get_session,
+    session_scope,
+)
+from duty_teller.db.repository import (
+    delete_duties_in_range,
+    get_or_create_user,
+    get_or_create_user_by_full_name,
+    get_duties,
+    insert_duty,
+    set_user_phone,
+)
+
+__all__ = [
+    "Base",
+    "User",
+    "Duty",
+    "UserCreate",
+    "UserInDb",
+    "DutyCreate",
+    "DutyInDb",
+    "DutyWithUser",
+    "get_engine",
+    "get_session_factory",
+    "get_session",
+    "session_scope",
+    "delete_duties_in_range",
+    "get_or_create_user",
+    "get_or_create_user_by_full_name",
+    "get_duties",
+    "insert_duty",
+    "set_user_phone",
+    "init_db",
+]
+
+
+def init_db(database_url: str) -> None:
+    """Create tables from metadata (Alembic migrations handle schema in production)."""
+    engine = get_engine(database_url)
+    Base.metadata.create_all(bind=engine)