perf(core): implement efficient bulk user deletion

Revamps the entire user deletion process to resolve critical performance bottlenecks that caused the web panel and database to freeze when removing multiple users.

- **Backend:** Core scripts (`kickuser.py`, `remove_user.py`) and the database layer are re-engineered to handle multiple users in a single, efficient batch operation using MongoDB's `delete_many`.
- **API:** A new `POST /api/v1/users/bulk-delete` endpoint is introduced for batch removals. The existing single-user `DELETE` endpoint is fixed to align with the new bulk logic.
- **Frontend:** The Users page now intelligently calls the bulk API when multiple users are selected, drastically improving UI responsiveness and reducing server load.

core/cli.py

@@ -184,23 +184,32 @@ def reset_user(username: str):
 
 
 @cli.command('remove-user')
-@click.option('--username', '-u', required=True, help='Username for the user to remove', type=str)
-def remove_user(username: str):
+@click.argument('usernames', nargs=-1, required=True)
+def remove_user(usernames: tuple[str]):
+    """Removes one or more users."""
+    if not usernames:
+        click.echo("No usernames provided.", err=True)
+        return
+        
     try:
-        cli_api.kick_user_by_name(username)
+        usernames_list = list(usernames)
+        cli_api.kick_users_by_name(usernames_list)
         cli_api.traffic_status(display_output=False)
-        cli_api.remove_user(username)
-        click.echo(f"User '{username}' removed successfully.")
+        cli_api.remove_users(usernames_list)
+        click.echo(f"Users '{', '.join(usernames)}' removed successfully.")
     except Exception as e:
         click.echo(f'{e}', err=True)
 
 @cli.command('kick-user')
-@click.option('--username', '-u', required=True, help='Username of the user to kick')
-def kick_user(username: str):
-    """Kicks a specific user by username."""
+@click.argument('usernames', nargs=-1, required=True)
+def kick_user(usernames: tuple[str]):
+    """Kicks one or more users by username."""
+    if not usernames:
+        click.echo("No usernames provided.", err=True)
+        return
+        
     try:
-        cli_api.kick_user_by_name(username)
-        # click.echo(f"User '{username}' kicked successfully.")
+        cli_api.kick_users_by_name(list(usernames))
     except Exception as e:
         click.echo(f'{e}', err=True)