🤖 fix: make image delete button visible (#568)

The delete button on pasted images was rendering behind the image and
wasn't visible or clickable.

## Problem

The button existed in the code but was completely hidden - the image
element was rendering on top of it despite attempts to use z-index and
absolute positioning.

## Solution

Switched from absolute positioning to CSS Grid layout. Both the image
and button are now placed in the same grid cell (`col-start-1
row-start-1`), which naturally creates proper layering without z-index
conflicts. The button is positioned in the top-right corner using
`self-start justify-self-end`.

## Visual Design

- Semi-transparent black circular button (bg-black/70)
- White × character
- Becomes more opaque on hover (bg-black/90)
- Small and unobtrusive in the corner

<img width="155" height="153" alt="image"
src="https://github.com/user-attachments/assets/1f5607f4-c934-4f17-a526-52bb7374d436"
/>


_Generated with `cmux`_

Author: ethanndickson

src/components/ImageAttachments.tsx

@@ -19,13 +19,18 @@ export const ImageAttachments: React.FC<ImageAttachmentsProps> = ({ images, onRe
       {images.map((image) => (
         <div
           key={image.id}
-          className="border-border-light bg-dark relative h-20 w-20 overflow-hidden rounded border"
+          className="border-border-light bg-dark group grid h-20 w-20 overflow-hidden rounded border"
         >
-          <img src={image.url} alt="Attached image" className="h-full w-full object-cover" />
+          <img
+            src={image.url}
+            alt="Attached image"
+            className="pointer-events-none col-start-1 row-start-1 h-full w-full object-cover"
+          />
           <button
             onClick={() => onRemove(image.id)}
             title="Remove image"
-            className="absolute top-1 right-1 flex h-5 w-5 cursor-pointer items-center justify-center rounded-full border-0 bg-black/70 p-0 text-sm leading-none text-white hover:bg-black/90"
+            className="col-start-1 row-start-1 m-0.5 flex h-5 w-5 cursor-pointer items-center justify-center self-start justify-self-end rounded-full border-0 bg-black/70 p-0 text-sm leading-none text-white hover:bg-black/90"
+            aria-label="Remove image"
           >
             ×
           </button>