Design Circular Queue

Design a circular queue (ring buffer) with a fixed capacity k. A circular queue reuses freed space at the front, so it never needs to shift elements.

• enQueue(value) inserts an element; returns true if successful, false if the queue is full.
• deQueue() removes an element from the front; returns true if successful, false if the queue is empty.
• Front() returns the front element, or -1 if empty.
• Rear() returns the last element, or -1 if empty.
• isEmpty() returns whether the queue is empty.
• isFull() returns whether the queue is full.

Implement the function circularQueue(k, operations) where k is the capacity and operations is a list of [op, ...args]: ["enQueue", v], ["deQueue"], ["Front"], ["Rear"], ["isEmpty"], ["isFull"]. Return the list of results, one per operation (use null for operations that return nothing - though every operation here returns a value).