SortZone: Animate dashboard items to fill space during window drag

Input from Gemini:

✦ The implementation of this feature involved several key refinements to the initial strategy to ensure a robust and high-quality UX.

1. Full-Geometry Animation Strategy: Instead of simply clearing styles, we implemented a system that calculates a specific "Target Layout" for the remaining dashboard items when a component is dragged out. This allows us to use CSS transitions on width, height, left, and top for a smooth "fill space" animation.

2. Robust Layout Calculation: We implemented calculateExpandedLayout which:

• Infers Gaps & Padding: Instead of parsing CSS, it analyzes the cached itemRects snapshot to mathematically derive the container's start/end offsets (padding) and the inter-item gaps. This ensures the "Expanded" layout perfectly respects the original design tokens (e.g., the 20px gaps in the AgentOS dashboard) without hardcoding them.
• Flex-Aware Distribution: It distributes the available space (total size minus offsets and gaps) proportionally based on the items' flex configs.

3. State Management & Restoration:

• Window Drag Start: We hide the placeholder and apply the calculated "Expanded" styles to the siblings.
• Re-entry (Drag Move): When dragging back into the zone, we restore the original layout snapshot (position and size) from itemRects and show the placeholder. This creates a seamless "snap back" effect.
• Cleanup (Drag End): We refactored onDragEnd to safely handle the complex state transitions (window vs. in-app), ensuring the drag proxy is removed and the component is either moved back (if dropped in-app) or left alone (if dropped in window), while correctly cleaning up the placeholder.

4. CSS Updates:

• Updated SortZone.scss to include width and height in the transition-property, enabling the smooth resizing effects.

This approach delivers a premium feel where the dashboard intelligently reflows to fill the void left by a detached window, and gracefully restores itself when the window returns.