Add Alembic for database migrations and initial migration scripts

- Created alembic.ini configuration file for Alembic migrations.
- Added README file for Alembic with a brief description.
- Implemented env.py for Alembic to manage database migrations.
- Created script.py.mako template for migration scripts.
- Added initial migration script to create database tables.
- Created a migration script to add initial plan and playlist data.
- Updated database initialization to run Alembic migrations.
- Enhanced credit service to automatically recharge user credits based on their plan.
- Implemented delete_task method in scheduler service to remove scheduled tasks.
- Updated scheduler API to reflect task deletion instead of cancellation.
- Added CLI tool for managing database migrations.
- Updated tests to cover new functionality for task deletion and credit recharge.
- Updated pyproject.toml and lock files to include Alembic as a dependency.

app/services/task_handlers.py

@@ -80,8 +80,11 @@ class TaskHandlerRegistry:
                 msg = f"Invalid user_id format: {user_id}"
                 raise TaskExecutionError(msg) from e
 
-            stats = await self.credit_service.recharge_user_credits(user_id_int)
-            logger.info("Recharged credits for user %s: %s", user_id, stats)
+            transaction = await self.credit_service.recharge_user_credits_auto(user_id_int)
+            if transaction:
+                logger.info("Recharged credits for user %s: %s credits added", user_id, transaction.amount)
+            else:
+                logger.info("No credits added for user %s (already at maximum)", user_id)
         else:
             # Recharge all users (system task)
             stats = await self.credit_service.recharge_all_users_credits()