Follow-up to the cherry-picked fix for #88391: the bare `streamdown` import
broke the plugin's side-load contract (vm-harness tests and the legacy-sdk
tmpdir loader can't resolve bare specifiers, and the runtime plugin door only
maps @hermes/plugin-sdk and react). Export Streamdown from the SDK instead,
feature-detect it in plugin.js like SkillsView/McpTab (plain-text fallback on
older desktops), and fix the indentation at the render site.
Teknium
577f5cf207