[FEATURE] Agents view: add search/filter to find sessions by name or prompt

Summary

The claude agents view (FleetView) has no way to search or filter the session list. When you have many sessions running or in history, there's no way to quickly find one by name or task description.

Desired behavior

Add a search/filter input to the agents view — similar to how the session picker (/resume) supports pressing / to filter by name or first prompt content. Ideally:

• Press / or start typing to enter search mode
• Filter sessions by name or task description in real time
• Works across all sessions visible in the current view

Current workaround

None — you have to scroll through the full list manually.

Related issues

• #60437 — sessions from daemon-fleet don't appear in agent view at all
• #61134 — request to group sessions by working directory