Feature: add responsive grid component

[ayangweb]

It would be useful to have a responsive grid component in gpui-kit, similar to [Ant Design Grid](https://ant.design/components/grid).

The main goal is to support breakpoint-based responsive layouts, for example:

• Automatically adjust the number of columns based on the available width.
• Support configurable breakpoints.
• Allow configuring the number of columns / span at different breakpoints.
• Support horizontal and vertical gaps.
• Avoid unnecessary empty space when the window size changes.

A typical use case would be displaying cards or other items in a responsive layout where the number of columns automatically changes as the available width changes.

For example:

Large window   → 4 columns
Medium window → 3 columns
Small window  → 2 columns
Very small    → 1 column

It would be great if gpui-kit could provide a reusable Grid component with behavior similar to Ant Design's Row / Col and breakpoint system.

Reference:
https://ant.design/components/grid