Monitor details panel should display the `description` field

Summary

The Monitor tool accepts a description parameter that documents what
the monitor is watching, but Claude Code's Monitor details panel does
not display this value. The panel shows Status / Runtime / Script /
Output, but no name or description.

Where it shows up today

The description does appear in the notification text when an event
fires or when the monitor ends (e.g., Monitor "Staging pipeline
(fresh plan)" stream ended), so the value is captured — it just is
not surfaced in the details panel.

Why it matters

When several monitors are arming and completing in close succession
(e.g., multiple CI pipelines being watched as fixes land), the
details panel is the natural place to disambiguate them. The Script
field is not a good substitute because all monitors of the same
class share the same script, just with different variables.

Suggested change

Render the description next to Status / Runtime in the Monitor
details panel

<img width="770" height="328" alt="Image" src="https://github.com/user-attachments/assets/75352ebe-43b0-4a87-9942-8dd5011aca2b" />