fix: read stackId from request body in CardApiController reorder

[guangningsun]

Fix: CardApiController reorder() ignores request body stackId

Issue: #7933

The reorder() method in CardApiController.php receives $stackId as a route parameter, but the actual target stack is passed in the request body. When the API is called with {"stackId": 37, "order": 0}, the card stays in its original stack.

Root Cause:

public function reorder($stackId, $order) {
    $card = $this->cardService->reorder(
        (int)$this->request->getParam('cardId'),
        (int)$stackId,  // <-- Uses route param, not body param
        ...
    );
}

Fix: Read stackId from the request body via php://input when the card needs to move to a different stack.

Testing:

1. Create a card in stack 36
2. Call PUT /stacks/36/cards/{id}/reorder with {"stackId": 37, "order": 0}
3. Card should now be in stack 37 (not stack 36)

Closes #7933