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.

pyproject.toml

@@ -6,6 +6,7 @@ readme = "README.md"
 requires-python = ">=3.12"
 dependencies = [
     "aiosqlite==0.21.0",
+    "alembic==1.16.5",
     "apscheduler==3.11.0",
     "bcrypt==4.3.0",
     "email-validator==2.3.0",