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/scheduler.py

@@ -144,6 +144,25 @@ class SchedulerService:
             logger.info("Cancelled task: %s (%s)", task.name, task_id)
             return True
 
+    async def delete_task(self, task_id: int) -> bool:
+        """Delete a scheduled task completely."""
+        async with self.db_session_factory() as session:
+            repo = ScheduledTaskRepository(session)
+
+            task = await repo.get_by_id(task_id)
+            if not task:
+                return False
+
+            # Remove from APScheduler first (job might not exist in scheduler)
+            with suppress(Exception):
+                self.scheduler.remove_job(str(task_id))
+
+            # Delete from database
+            await repo.delete(task)
+
+            logger.info("Deleted task: %s (%s)", task.name, task_id)
+            return True
+
     async def get_user_tasks(
         self,
         user_id: int,