Better support for images/visualizations in workflow output

[brandomr]

You can hack in image support in workflow outputs via prompting such as:

Write files to your current working directory, but reference them with the /files/ prefix when displaying in markdown (e.g., save as 'my_viz.png' but display as '/files/my_viz.png').

Ensure that display visualizations are rendered inline as html images with the following css: width: 85%; display: block; margin: auto;. For example:

<img src="/files/my_viz.png" alt="my viz" style="width:85%; display:block; margin:auto;" />

This only works if this prompt is included at the relevant workflow stages and in the agent's top level prompt.

Proposal: this could be included in the workflow tool docstrings to enable global support.