Feat: Implement Neo.container.Spatial (Pan/Zoom Whiteboard)

[tobiu]

Create a container designed for infinite 2D spatial layouts (whiteboard style).

Features:

1. Infinite Pan: Drag background to pan. Integrate GridDragScroll physics for momentum.
2. Vector Zoom: Wheel/Pinch to scale the view.
3. Virtualization (Optional/Phase 2): Culling items outside the viewport for massive scale.

Use Cases:

• Node Editors (Blueprints)
• Whiteboards
• Interactive Maps (Non-GIS)
• Desktop-like Window Managers (inside a browser tab)