Images in webchat markdown messages (e.g. agent screenshots) fail to
load because the img component passes local filesystem paths directly
as <img src>, which the browser cannot resolve.
The chain-of-thought component already handles this via
resolveMediaUrl(), but the ReactMarkdown img override did not.
Now non-HTTP/data src values are proxied through
/api/workspace/raw-file?path=... so the server can resolve and serve
local files.
92c76dc4ce