[FEATURE]:Support base64 decoding in the harness to post images to the agent

[vampaz]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

As a user, I want to be able to paste base64 encoded images into the TUI and have the app decode them and attach them to the prompt.

This is useful since a web screenshot tool has no other way to share images with opencode.

Acceptance criteria

When data:image/png;base64,iVBORw0KGgoAAAANSU.... is found in the prompt, it should be decoded and an image inserted in the call

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• AI_APICallError - base64 encoded image pasted #4983: AI_APICallError - base64 encoded image pasted - discusses issues with pasted base64 encoded images being included in subsequent messages
• [FEATURE]:: paste images directly into the chat UI like another chat cllients #12181: [FEATURE]:: paste images directly into the chat UI like another chat clients - requests ability to paste images from clipboard

Feel free to ignore if none of these address your specific case.

[github-actions]

To stay organized issues are automatically closed after 90 days of no activity. If the issue is still relevant please open a new one.