Expose scripted custom previewer tabs on MCP (get_flow_detail / get_flows)

Description

Scripted custom views already exist in the GUI:

request.customPreviewerTabs["Role"] = JSON.stringify({ model: request.body.model }, null, 2);

MCP get_flow_detail returns headers, body preview, query, cookies. It does not return customPreviewerTabs, Comment, or Color. An agent has to re-parse the raw body and cannot see the view a human already built.

Why this feature/change is important?

Proxyman MCP is how coding agents drive a live session. If scripts compute a view for the GUI, that same view should be a first-class MCP field. Otherwise humans and agents debug two different representations of the same flow.

Suggested behavior

• Include customPreviewerTabs (request and response), comment, and color on get_flow_detail.
• Optionally list those keys on get_flows / filter_flows so an agent can filter without opening every body.
• Same script, two consumers: GUI tab and MCP. No extra header mutation.