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.

migrate.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""Database migration CLI tool."""
+
+import argparse
+import sys
+from pathlib import Path
+
+from alembic import command
+from alembic.config import Config
+
+
+def main() -> None:
+    """Main CLI function for database migrations."""
+    parser = argparse.ArgumentParser(description="Database migration tool")
+    subparsers = parser.add_subparsers(dest="command", help="Migration commands")
+
+    # Upgrade command
+    upgrade_parser = subparsers.add_parser("upgrade", help="Upgrade database to latest revision")
+    upgrade_parser.add_argument(
+        "revision",
+        nargs="?",
+        default="head",
+        help="Target revision (default: head)"
+    )
+
+    # Downgrade command
+    downgrade_parser = subparsers.add_parser("downgrade", help="Downgrade database")
+    downgrade_parser.add_argument("revision", help="Target revision")
+
+    # Current command
+    subparsers.add_parser("current", help="Show current revision")
+
+    # History command
+    subparsers.add_parser("history", help="Show revision history")
+
+    # Generate migration command
+    revision_parser = subparsers.add_parser("revision", help="Create new migration")
+    revision_parser.add_argument("-m", "--message", required=True, help="Migration message")
+    revision_parser.add_argument("--autogenerate", action="store_true", help="Auto-generate migration")
+
+    args = parser.parse_args()
+
+    if not args.command:
+        parser.print_help()
+        sys.exit(1)
+
+    # Get the alembic config
+    config_path = Path("alembic.ini")
+    if not config_path.exists():
+        print("Error: alembic.ini not found. Run from the backend directory.")
+        sys.exit(1)
+
+    alembic_cfg = Config(str(config_path))
+
+    try:
+        if args.command == "upgrade":
+            command.upgrade(alembic_cfg, args.revision)
+            print(f"Successfully upgraded database to revision: {args.revision}")
+
+        elif args.command == "downgrade":
+            command.downgrade(alembic_cfg, args.revision)
+            print(f"Successfully downgraded database to revision: {args.revision}")
+
+        elif args.command == "current":
+            command.current(alembic_cfg)
+
+        elif args.command == "history":
+            command.history(alembic_cfg)
+
+        elif args.command == "revision":
+            if args.autogenerate:
+                command.revision(alembic_cfg, message=args.message, autogenerate=True)
+                print(f"Created new auto-generated migration: {args.message}")
+            else:
+                command.revision(alembic_cfg, message=args.message)
+                print(f"Created new empty migration: {args.message}")
+
+    except Exception as e:
+        print(f"Error: {e}")
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()