🎨 Palette: Add ARIA label to remove attachment button

[thirdeyenation]

💡 What: Added aria-label and title to the remove attachment <button> in webui/components/chat/attachments/inputPreview.html.
🎯 Why: The remove button only contained a visual × character, meaning screen readers would not announce its purpose properly, nor did it have a hover tooltip for sighted users relying on pointers.
📸 Before/After: N/A - Visually identical.
♿ Accessibility: Screen readers will now announce the button as "Remove attachment" rather than reading "times" or ignoring it.

This change adheres to Palette's goals of small, high-impact UX improvements and addresses a clear accessibility need.

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PR created automatically by Jules for task 13523251549126658047 started by @thirdeyenation

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