web: attachment remove button is inaccessible on touch devices

Summary

Image attachments added to the web prompt cannot be removed reliably on touch-only devices because the remove button is fully transparent until CSS group-hover activates.

Environment

• opencode version: v2.0.3
• OS: Windows 10.0.26200.9445 server; Android client on Xiaomi 17 Pro Max
• Terminal: OpenCode web UI in Android Chrome
• Shell: C:\WINDOWS\system32\cmd.exe on the server
• Install/channel: OpenCode Desktop stable, bundled CLI 2.0.3
• Active plugins: global opencode-goal.ts and opencode-go-usage.ts

Reproduction

1. Open the OpenCode web UI in Chrome on an Android touch-only device.
2. Add an image to the prompt composer.
3. Try to remove the attached image before sending the prompt.

Expected Behavior

The attachment should expose a visible, touch-accessible remove control, allowing it to be removed before the prompt is sent.

Actual Behavior

The image thumbnail is visible, but there is no usable remove control on the touch device. The attachment can be added but cannot be removed without discarding or reloading the draft.

Additional Context

The current upstream component renders the button with:

class="... opacity-0 group-hover:opacity-100 transition-opacity"

Source: packages/session-ui/src/v2/components/prompt-input/index.tsx, current main commit e03db9b, around lines 445-452.

The click handler and aria-label already exist, so this appears to be a touch-accessibility/visibility issue rather than missing removal logic. A possible direction is to keep the button visible for coarse pointers/touch devices while retaining hover behavior for mouse input.

The issue is consistently reproducible. No project data or model/provider behavior is involved.