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/api/v1/scheduler.py

@@ -129,7 +129,7 @@ async def update_task(
 
 
 @router.delete("/tasks/{task_id}")
-async def cancel_task(
+async def delete_task(
     task_id: int,
     current_user: Annotated[User, Depends(get_current_active_user)] = ...,
     scheduler_service: Annotated[
@@ -137,7 +137,7 @@ async def cancel_task(
     ] = ...,
     db_session: Annotated[AsyncSession, Depends(get_db)] = ...,
 ) -> dict:
-    """Cancel a scheduled task."""
+    """Delete a scheduled task completely."""
     repo = ScheduledTaskRepository(db_session)
     task = await repo.get_by_id(task_id)
 
@@ -148,11 +148,11 @@ async def cancel_task(
     if task.user_id != current_user.id and not current_user.is_admin:
         raise HTTPException(status_code=403, detail="Access denied")
 
-    success = await scheduler_service.cancel_task(task_id)
+    success = await scheduler_service.delete_task(task_id)
     if not success:
-        raise HTTPException(status_code=400, detail="Failed to cancel task")
+        raise HTTPException(status_code=400, detail="Failed to delete task")
 
-    return {"message": "Task cancelled successfully"}
+    return {"message": "Task deleted successfully"}
 
 
 # Admin-only endpoints