fix(opencode): validate clipboard content type on Linux

[h0wdee]

Summary

• Validate clipboard content using sniffAttachmentMime() before treating as PNG on Linux
• Fixes text being incorrectly identified as image when pasting via Ctrl+V

Root Cause

On Linux, xclip -selection clipboard -t image/png -o outputs raw bytes even when clipboard contains text. The code only checked byteLength > 0, so text (e.g. Unicode like ¯\_(ツ)_/¯) was labeled as image/png and sent to the model, which failed with "could not process image".

Fix

Use the existing sniffAttachmentMime() function from media.ts to check for PNG magic bytes before returning clipboard content as an image. This is the same validation pattern used in the read tool.

Verification

1. Copy text with Unicode: echo '¯\_(ツ)_/¯' | xclip -selection c
2. Ctrl+V in OpenCode TUI
3. Text now pastes correctly instead of failing with "could not process image"

Fixes#23458

[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Related PR Found:

• PR feat(tui): improve clipboard paste and drag-and-drop file handling on Linux #14552: "feat(tui): improve clipboard paste and drag-and-drop file handling on Linux"
  • feat(tui): improve clipboard paste and drag-and-drop file handling on Linux #14552
  • Why related: This PR also addresses clipboard handling on Linux. It may have overlapping concerns with the clipboard content validation fix, though it appears to be a broader feature PR rather than a bug fix. Worth reviewing to ensure no conflicts with the drag-and-drop changes.

[h0wdee]

Updated PR description to match the template. All checks are passing. Could a maintainer remove the needs:compliance label? Thanks!

[github-actions]

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