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/handlers/errors.py

@@ -0,0 +1,16 @@
+"""Global error handler: log exception and notify user."""
+
+import logging
+
+from telegram import Update
+from telegram.ext import ContextTypes
+
+logger = logging.getLogger(__name__)
+
+
+async def error_handler(
+    update: Update | None, context: ContextTypes.DEFAULT_TYPE
+) -> None:
+    logger.exception("Exception while handling an update")
+    if isinstance(update, Update) and update.effective_message:
+        await update.effective_message.reply_text("Произошла ошибка. Попробуйте позже.")