Fix memory leak in Resizer.svelte event listeners

[Copilot]

Event listeners added to document during mouse/touch drag operations in Resizer.svelte were never cleaned up if the component unmounted mid-drag, causing memory leaks.

Changes

• Add onDestroy lifecycle hook to remove document-level event listeners on unmount
• Clean up both mouse (mousemove, mouseup) and touch (touchmove, touchend) listeners
• Reset body styles (cursor, userSelect) if unmounting during active drag

onDestroy(() => {
    document.removeEventListener("mousemove", handleMouseMove);
    document.removeEventListener("mouseup", handleMouseUp);
    document.removeEventListener("touchmove", handleTouchMove);
    document.removeEventListener("touchend", handleTouchEnd);
    if (isDragging) {
        document.body.style.cursor = "";
        document.body.style.userSelect = "";
    }
});

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